Discuss ethical considerations in screening Cheryl Reeves, MS, MLS · 2018-04-01 · Slide 13: Screening versus Diagnostic Tests Diagnostic tests, on the other hand, are used to determine

Module 4: Screening

TRANSCRIPT

Page 1

Slide 1: Introduction

The screening module is one of a series created

through the funding from the Centers for

Disease Control and Prevention and the

Association for Prevention Teaching and

Research.

Slide 2: Acknowledgements

Slide 3: Presentation Objectives

The objectives of this presentation are as

follows: Define screening and the appropriate

conditions for screening; evaluate screening

tests in terms of validity, results, and

generalizability; evaluate the effectiveness of a

screening program; discuss common biases in

evaluating screening programs; and discuss

common ethical considerations in screening.

Slide 4: Introduction to Screening

We will begin with an overview of screening.

Developed through the APTR Initiative to Enhance Prevention and Population

Health Education in collaboration with the Brody School of Medicine at East

Carolina University with funding from the Centers for Disease Control and

Prevention

Developed through the APTR Initiative to Enhance Prevention and Population

Health Education in collaboration with the Brody School of Medicine at East

Carolina University with funding from the Centers for Disease Control and

Prevention

APTR wishes to acknowledge the following individuals that developed this module:

Anna Zendell, PhD, MSWCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

Joseph Nicholas, MD, MPHUniversity of Rochester School of Medicine

Mary Applegate, MD, MPHUniversity at Albany School of Public Health

Cheryl Reeves, MS, MLSCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the

Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module

represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease

Control and Prevention or the Association for Prevention Teaching and Research.

APTR wishes to acknowledge the following individuals that developed this module:

Anna Zendell, PhD, MSWCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

Joseph Nicholas, MD, MPHUniversity of Rochester School of Medicine

Mary Applegate, MD, MPHUniversity at Albany School of Public Health

Cheryl Reeves, MS, MLSCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the

Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module

represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease

Control and Prevention or the Association for Prevention Teaching and Research.

1. Define screening and identify appropriate conditions for screening

2. Evaluate screening tests in terms of their validity, results and generalizability

3. Evaluate the effectiveness of a screening program and discuss the common biases

4. Discuss ethical considerations in screening

1. Define screening and identify appropriate conditions for screening

2. Evaluate screening tests in terms of their validity, results and generalizability

3. Evaluate the effectiveness of a screening program and discuss the common biases

4. Discuss ethical considerations in screening

Module 4: Screening

TRANSCRIPT

Page 2

Slide 5: Oprah’s Full Body Scan

Take a few minutes to watch a video clip related

to screening. Oprah Winfrey has completed a

full body scan. Fully body scans are one of the

newer “fads” in healthcare. Some are done in a

medical office and others are conducted out of

mobile vans. Oprah is discussing the results of

her scan on national TV with her doctor. As you

watch the clip and complete this module think about implications for patient screening.

Are there medical concerns that may result from using this technology? How about any

ethical issues? What barriers to accessing full body scans may exist and for what groups

of people? In particular, think about what happens after the scan. Every human body

has some imperfections. Do these imperfections necessarily require medical

intervention, or may uncovering them cause the patient unnecessary physical or

psychological harm?

Slide 6: Preventive Medicine & Public Health

Preventive medicine and public health share

many common goals. First and foremost, both

strive to promote quality of life by preventing

disease. This goal is accomplished through

health promotion programs and prevention of

common diseases, like diabetes, cancer, and

injuries. The difference is that preventive

medicine works toward these goals at both the individual patient level and the

population level. Public health’s focus is at the population level. [The distinguishing

factor about preventive medicine that makes it special is its focus on populations!]

As you watch this clip and complete the module, think about the implications for patient screening based on this technology

Medical concerns?

Ethical considerations?

Access issues?

Informed decision-making after screening?

http://www.youtube.com/watch?v=6hlMlbmcSHg

As you watch this clip and complete the module, think about the implications for patient screening based on this technology

Medical concerns?

Ethical considerations?

Access issues?

Informed decision-making after screening?

http://www.youtube.com/watch?v=6hlMlbmcSHg

Share common goals

Enhance quality of life of patients

▪ Health promotion

▪ Disease and injury prevention

Preventive medicine promotes these goals at the individual and population levels, while public health focuses on populations.

Share common goals

Enhance quality of life of patients

▪ Health promotion

▪ Disease and injury prevention

Preventive medicine promotes these goals at the individual and population levels, while public health focuses on populations.

Module 4: Screening

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Slide 7: Prevention – Brief Overview

Prevention occurs at three levels. The first level

is primary prevention. These are preventive

measures that are undertaken to prevent the

onset of illness and injury. This is done through

the elimination of causal risk factors or by

increasing resistance to the condition. An

example of primary prevention is childhood

vaccination against infectious disease. Secondary prevention entails measures that lead

to early diagnosis and prompt treatment of illness or injury. Here we try to interrupt the

disease process by detecting and treating it before symptoms emerge. For a test to have

the “screening” characteristic it must be done in the non-symptomatic phase of the

disease. Cancer screening is an example of secondary prevention. Tertiary prevention

involves measures aimed at minimizing disability after disease symptoms have appeared.

Cardiac rehabilitation following a diagnosis of heart failure is an example of tertiary

prevention.

Slide 8: Screening Defined

Screening is defined as the presumptive

identification of an unrecognized disease or

defect through tests, exams, or other procedures

that can be applied rapidly and easily. Screening

tests differentiate apparently healthy persons

who may have a disease from those who

probably don’t have the disease.

Primary Prevention

Secondary Prevention

Tertiary Prevention

McKenzie et al.: 2008

Primary Prevention

Secondary Prevention

Tertiary Prevention

McKenzie et al.: 2008

Presumptive identification of an unrecognized disease through tests, examinations, or other procedures which can be applied rapidly

Screening tests sort out apparently well persons who probably have a disease from those who probably do not.

Presumptive identification of an unrecognized disease through tests, examinations, or other procedures which can be applied rapidly

Screening tests sort out apparently well persons who probably have a disease from those who probably do not.

Module 4: Screening

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Page 4

Slide 9: Importance of Screening

Screening is widely considered the bedrock of

secondary prevention. Periodic health screening

can lead to early detection and diagnosis of a

disease. This early detection then leads to

earlier treatment with a goal of decreasing

mortality and morbidity related to that disease.

In the case of infectious diseases, screening can

also break the chain of transmission and prevent development of new cases. Screenings

can be cost-effective if the disease is common enough and the test is accurate enough.

It’s also cost-effective if affordable treatments that work are accessible to those patients

whom test positive. Because we may develop diseases at many points throughout our

lifespan, many screenings are only effective if done periodically.

Slide 10: Screening-Diagnosis Connection

The best screening protocols generally

incorporate a patient history, physical exam, and

laboratory test. Pre-test probability, also known

as demographically determined risk, is probably

the biggest reason to screen someone. Positive

results of the screening test will trigger a

diagnostic work-up and preventive or treatment

interventions.

Slide 11: Screening versus Diagnostic Tests

Many people use the terms screening and

diagnosis interchangeably. They are not the

same.

Early detection

Leads to early treatment

Can lead to a decrease in morbidity and mortality

Can break the chain of transmission and development of new cases

Is often cost-effective

The human body is continually changing

Jekel et al:, 1996; McKenzie et al:, 2008; Londrigan &

Lewenson: 2011

Early detection

Leads to early treatment

Can lead to a decrease in morbidity and mortality

Can break the chain of transmission and development of new cases

Is often cost-effective

The human body is continually changing

Jekel et al:, 1996; McKenzie et al:, 2008; Londrigan &

Lewenson: 2011

Screening starts before diagnosis

History questions

Physical exam findings

Lab tests

Pre-test probability

Results of screening trigger diagnostic work-up and preventive interventions

Jekel et al:, 1996; McKenzie et al:, 2008

Screening starts before diagnosis

History questions

Physical exam findings

Lab tests

Pre-test probability

Results of screening trigger diagnostic work-up and preventive interventions

Jekel et al:, 1996; McKenzie et al:, 2008

Diagnostic Test

Screening Test ≠ Diagnostic Test

Screening Test ≠

Module 4: Screening

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Page 5


Screening tests are used for a presumptive

identification of an unrecognized disease or

illness.


Diagnostic tests, on the other hand, are used to

determine the presence or absence of a disease

when the patient is showing symptoms of the

disease OR has been targeted through a positive

screening test. In some circumstances, the same

test can function as either a screening or

diagnostic test.

Slide 14: Characteristics of a Good Screening

Test

A good screening test must meet several

important criteria. It needs to be simple and

quick to administer. It should be inexpensive

and safe to use. It also needs to be readily

available, along with an accessible plan of

treatment in place in case of positive results. A

good screen must be acceptable to the population in which it will be used. It must also

be well researched and proven to be valid, reliable, and to have good predictive values.

We will discuss these criteria in more detail a bit later.

Slide 15: Common Screening Tests

Next, we will discuss some common screening

tests.

Diagnostic Test

Screening Test ≠

Identifies asymptomatic people who may have a disease

Diagnostic Test

Screening Test ≠

Identifies asymptomatic people who may have a disease

Screening Test ≠Identifies asymptomatic people who may have a disease

Diagnostic Test

Determines presence or absence of disease when patient shows signs or symptoms

Screening Test ≠Identifies asymptomatic people who may have a disease

Diagnostic Test

Determines presence or absence of disease when patient shows signs or symptoms

Simple Rapid Inexpensive Safe Available Acceptable

Simple Rapid Inexpensive Safe Available Acceptable

Module 4: Screening

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Slide 16: Common Disease Screenings

Take a few moments to review this list of

screenings commonly conducted in the US. Do

you know what conditions they screen for?

Slide 17: Common Disease Screenings

Medical practitioners have access to numerous

screenings for potentially life-threatening

conditions. We will briefly discuss some

common ones and then focus on several in more

detail. All women age 21 or older should receive

Pap smears to test for cervical cancer. Pap

smears may be administered even earlier for

younger women and girls who are sexually active. These are routine ongoing screens,

usually performed every 1-3 years. Pap smears may be done more often if abnormalities

are found, or if a family history is reported. A fasting blood sugar test is conducted for

anyone at any age at risk for diabetes, for instance pregnant women, people who are

overweight, or those with a family history of diabetes. The fecal occult blood test is a

common screening for colorectal cancer. We will learn more about this a bit later. Blood

pressure is taken at annual exams and during each visit to the primary care provider. If

hypertension is found, patients may be advised to come regularly for blood pressure

tests. In some cases, people may receive blood pressure cuffs which enable them to

check and log their blood pressure daily. Osteoporosis or osteopenia are often

diagnosed in adults over age fifty, or in adults of any age with metabolic or eating

disorders. Bone densitometry is indicated for women over the age of 65. People with a

family history of these conditions or other risk factors may also have a bone density scan.

Men over the age of 50 can be screened for prostate cancer, through an annual PSA test

(or prostate-specific antigen). The typical tuberculosis screening is a TB skin test, also

called a purified protein derivative or PPD test. TB tests are mandated for children and

adults attending educational institutions. Anyone working in a healthcare setting or

correctional facility is also mandated to be tested annually. Mammography is used to

screen for breast cancer. The guidelines for screening are quite controversial. We will

discuss these more in a few moments.

Pap smear screens for ___________________________

Fasting blood sugar screens for _________________

Fecal occult blood test screens for ______________

Blood pressure screens for ______________________

Bone densitometry screens for _________________

PSA test screens for _____________________________

PPD test screens for _____________________________

Mammography screens for ______________________

USPSTF: 2009

Pap smear screens for ___________________________

Fasting blood sugar screens for _________________

Fecal occult blood test screens for ______________

Blood pressure screens for ______________________

Bone densitometry screens for _________________

PSA test screens for _____________________________

PPD test screens for _____________________________

Mammography screens for ______________________

USPSTF: 2009

Pap smear screens for cervical cancer

Fasting blood sugar screens for diabetes

Fecal occult blood test screens for colorectal cancer

Blood pressure screens for hypertension

Bone densitometry screens for osteoporosis & osteopenia

PSA test screens for prostate cancer

PPD test screens for tuberculosis

Mammography screens for breast cancer.

USPSTF: 2009

Pap smear screens for cervical cancer

Fasting blood sugar screens for diabetes

Fecal occult blood test screens for colorectal cancer

Blood pressure screens for hypertension

Bone densitometry screens for osteoporosis & osteopenia

PSA test screens for prostate cancer

PPD test screens for tuberculosis

Mammography screens for breast cancer.

USPSTF: 2009

Module 4: Screening

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Slide 18: Common Wellness Screenings

There are numerous federal, state, and local

initiatives to fight obesity in children and adults.

Weight is one of the standard screens that occur

at each medical visit. In many cases, BMI or

body mass index is also calculated. A standard

oral examination can identify dental caries

(cavities) as well as oral cancers and many other

conditions. The NIDA-Modified Alcohol, Smoking, and Substance Involvement Screening

Test is a commonly used screening to detect the use and abuse of alcohol, tobacco, and

other legal and illegal drugs. The screening test starts out with preliminary questions to

assess use and then asks questions to identify abuse and/ or dependence. Now, let’s

delve into more detail on a few screenings.

Slide 19: Breast Cancer Screening

There has been a great deal of controversy

recently on the protocols for breast cancer

screening. Standard protocol for decades has

been annual mammogram for women age 40

and older. Younger women are also screened

annually if there is a family history of breast

cancer. In 2009, the United States Preventive

Services Task Force reviewed the medical evidence on regular use of mammograms.

Issues such as population prevalence, costs, and consequences of false positive results

were considered. Based on this review, the recommendations changed in late 2009.

Mammograms are no longer recommended for women under 50, unless they and their

providers feel it’s necessary. Women 50 and older are now urged to get mammograms

every other year. The opposition to the revised mammogram recommendations has

been strong. Many healthcare providers’ organizations, particularly radiologists and

breast surgeons, have long advocated for yearly screenings. They have worked hard to

promote the importance of regular mammograms. For more information on the reasons

behind the controversy, please see articles appended in the resources section.

Obesity

Dental caries, oral cancer

Drugs, Alcohol, and Tobacco

Weight, Body Mass Index

Oral examination

Urine test, NMASSIST, or Flagerstrom Tolerance Test for Nicotine Dependency

http://www.drugabuse.gov/NIDAMED/screening/

Obesity

Dental caries, oral cancer

Drugs, Alcohol, and Tobacco

Weight, Body Mass Index

Oral examination

Urine test, NMASSIST, or Flagerstrom Tolerance Test for Nicotine Dependency

http://www.drugabuse.gov/NIDAMED/screening/

Standard practice Annual mammograms for women age 40+ years

Start earlier if family history of breast cancer

2009 US Preventive Services Task Force (USPSTF) recommendations Mammograms not universal for women age 40-50 years

Bi-annual mammograms for women 50+ years

Cost-benefit analysis False positives

Unnecessary invasive procedures

Standard practice Annual mammograms for women age 40+ years

Start earlier if family history of breast cancer

2009 US Preventive Services Task Force (USPSTF) recommendations Mammograms not universal for women age 40-50 years

Bi-annual mammograms for women 50+ years

Cost-benefit analysis False positives

Unnecessary invasive procedures

Module 4: Screening

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Slide 20: Colon Cancer Screening

We have a number of screening options available

for colorectal cancer. The gold standard, or most

accurate screening, is the colonoscopy. The

colonoscopy allows immediate biopsy and

immediate excision of any lesions. However, it’s

also the most expensive and is very dependent

on patient preparation and practitioner

expertise. Sigmoidoscopy examines the most distal part of the colon. While this

screening tool allows immediate biopsy and excision, it can only assess part of the colon

and misses polyps that are beyond its range. Virtual colonoscopies, commonly called CT

colonoscopies and barium enemas both require the same bowel preparation as the

colonoscopy; however, there is no ability to do biopsies or excisions during the

procedures. These screenings involve significant radiation exposure. Fecal occult blood

testing (FOBT) is an easy, inexpensive, and non-invasive screening tool. Fecal testing is,

however, less sensitive and specific than the other tests we have mentioned. Occult

blood may be due to other health conditions, leading to many false positive results. New

fecal DNA tests remain less sensitive than the other tests mentioned, but they have

fewer false positive test results than FOBT. Recommendations for age of initial screening

and frequency of screening vary by test and family history.

Slide 21: Case Study

You will find a case study on Colorectal Cancer

Screening in the small group activities section of

this module. This case study, used in classes

across the United States, will allow you to

practice evaluating diagnostic tests and

screening programs. You will also discuss

concepts related to preventive medicine. You

will be able to apply these concepts at the individual patient and population levels.

Multiple screening options

Colonoscopy – gold standard

Sigmoidoscopy

Virtual colonoscopy – CT colonoscopy

Barium enema

Fecal testing – occult blood, DNA test

Recommended age, frequency vary by test and family history

Multiple screening options

Colonoscopy – gold standard

Sigmoidoscopy

Virtual colonoscopy – CT colonoscopy

Barium enema

Fecal testing – occult blood, DNA test

Recommended age, frequency vary by test and family history

Practice evaluation of diagnostic test characteristics and screening programs

Discuss prevention concepts

Apply this at patient and population level

Practice evaluation of diagnostic test characteristics and screening programs

Discuss prevention concepts

Apply this at patient and population level

Module 4: Screening

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Slide 22: Newborn Screening

Newborn screening is mandatory in all states. It

looks for serious metabolic, hormonal,

hematologic, and infectious conditions. States

vary widely in what diseases they test for and

how many. For example, NY tests for over 40

conditions, including HIV. Newborn screening

involves a heel prick blood test done 24-48 hours

after birth. Most states now use a tandem mass spectrometer to test blood, which tests

for many metabolic conditions with one drop of blood. The 24 to 48-hour window of

time is important. If testing is done too early, the presence of diseases may not show up

in the baby’s blood. Some of the more common screens include: phenylketonuna(PKU),

galactosemia, medium-chain acylcarnitine deficiency (MCAD), sickle cell anemia, and HIV.

In addition to a state’s mandated tests, family history or ethnicity may indicate a need

for additional screens. Non-mandatory screens are not paid for by the state. They may or

may not be covered under a family’s personal health insurance.

Slide 23: Evaluation of Screening Tests

Now, we will briefly discuss how screening tests

are evaluated for use.

Mandatory universal screen for disorders, including metabolic, hormonal, hematologic, and infectious conditions

States vary in what diseases they test for

Heel prick blood test 24-48 hours post birth - if done too early, metabolic disease may not show up in blood

Family history may indicate need for additional screens

Mandatory universal screen for disorders, including metabolic, hormonal, hematologic, and infectious conditions

States vary in what diseases they test for

Heel prick blood test 24-48 hours post birth - if done too early, metabolic disease may not show up in blood

Family history may indicate need for additional screens

Module 4: Screening

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Slide 24: Evaluating Tests

Two central concepts in evaluation of tests are

validity and reliability. Validity is defined as how

well the test result corresponds to the “true”

condition of the patient, i.e. whether or not the

person has the disease. Reliability, on the other

hand, evaluates how consistent or reproducible

the test results are over time or under different

testing conditions. For this module, we will not discuss validity in detail, as the concepts

are more relevant to research studies than clinical tests. To learn more about validity,

see the Resources Section.

Slide 25: Characteristics of a Screening Test

Testing both validity and reliability is important.

You can have a test that is quite reliable over

time and across groups, but that isn’t valid. It

misses the mark. Likewise, you can have a test

that is valid, but not very reliable for certain

groups or in certain testing situations. We want

screening tests that are both valid measures of

what is being tested and reliable in various groups and at all times.

Slide 26: Reliability

Reliability, commonly referred to as consistency,

is the ability of a test to yield the same results

with repeated measurements. Put another way,

reliability is the degree to which results are free

from error across testing occasions. If we have a

large random error in a test, we see decreased

reliability.

Reliability and validity are central concepts in evaluating tests

Distinction between reliability and validity

Reliability: consistency of test at different times or under differing conditions

Validity: how well test distinguishes between who has disease and who does not

Fortune & Reid: 1998; Jekel et al:, 1996

Reliability and validity are central concepts in evaluating tests

Distinction between reliability and validity

Reliability: consistency of test at different times or under differing conditions

Validity: how well test distinguishes between who has disease and who does not

Fortune & Reid: 1998; Jekel et al:, 1996

VALIDITY and RELIABILITY

Fortune & Reid: 1998

VALIDITY and RELIABILITY

Fortune & Reid: 1998

Also known as consistency

Ability to yield the same results with repeated measurements of same construct

Degree to which results are free from random error

Jekel: 1996; Al-Eisa: 2009

Also known as consistency

Ability to yield the same results with repeated measurements of same construct

Degree to which results are free from random error


Module 4: Screening

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Slide 27: Common Types of Reliability

Intra-subject reliability refers to the consistency

of measurement scores taken on the same

subject across testing occasions. We are

evaluating the degree of change in subject

performance on the test from one time to

another.


Intra-rater reliability refers to the consistency of

measurements taken by the same tester on two

or more testing occasions.


Inter-rater reliability is considered one of the

most important indices of reliability for

screening tools. Here we are looking at the

consistency of measurement scores taken by two

different testers.


Instrument reliability is another important

indicator of reliability. It refers to the internal

consistency of the measurement tool itself. All

of these forms of reliability serve an important

purpose in evaluating screening and diagnostic

tests.


Intra-subject


Intra-subject

Intra-subject

Intra-rater


Intra-subject

Intra-rater


Intra-subject

Inter-rater

Intra-rater


Intra-subject

Inter-rater

Intra-rater


Intra-subject

InstrumentInter-rater

Intra-rater


Intra-subject

InstrumentInter-rater

Intra-rater


Module 4: Screening

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Page 12

Slide 31: Sensitivity

We will now talk about sensitivity and specificity.

These concepts relate to validity, or how well a

test result reflects reality. Sensitivity evaluates

the ability to find the patients who do have the

disease. In other words, sensitivity is the percent

of people with the disease who are correctly

identified. A sensitive test will reduce or

eliminate false negatives. False negatives are test results that suggest absence of the

disease when the disease is in fact present. These are also called beta or Type II errors.

We want to aim for high sensitivity when the consequences of a missed diagnosis are

serious. An example might be screening donated blood for the presence of HIV. An easy

way to remember sensitivity is the SNOUT acronym. Sensitive test with Negative results

rules OUT disease.

Slide 32: Specificity

Specificity evaluates the ability to identify which

patients do not have the disease. Specificity

seeks to reduce or eliminate false positives. False

positives are test results that suggest presence

of disease when the disease is not actually

present. They are also commonly called alpha or

type I errors. We want to aim for high specificity

when there are serious adverse consequences for patients incorrectly identified as

having the disease. For example we want a high degree of specificity in breast tissue

biopsy outcomes to confirm cancer before doing a mastectomy or starting chemotherapy

or radiation. If the specificity for a test is low, we need follow-up testing to rule out false

positives. An easy acronym to remember specificity is SPIN. Specific test with Positive

results rules IN disease. We want screening tests to be both sensitive and specific.

Measures validity of screening tests

Ability to identify those with disease correctly

Minimizes false negatives – if test highly sensitive

SNOUT – Sensitive test with Negative result rules OUT disease

Measures validity of screening tests

Ability to identify those with disease correctly

Minimizes false negatives – if test highly sensitive

SNOUT – Sensitive test with Negative result rules OUT disease

Ability to identify those without disease correctly

Minimizes false positives – if test highly specific

SPIN – Specific test with Positive result rules INdisease

Ability to identify those without disease correctly

Minimizes false positives – if test highly specific

SPIN – Specific test with Positive result rules INdisease

Module 4: Screening

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Page 13

Slide 33: Relationship Between Sensitivity and

Specificity

This table shows the relationship between

sensitivity and specificity in prostate-specific

antigen (PSA) levels. For screening tests whose

results fall along a continuum of values, such as

the PSA, there is a trade-off between specificity

and sensitivity, based on where you set the “cut-

off” score. In setting the cut-off point, we need to balance the risks of Type I and Type II

errors for a given disease.

Slide 34: The 2x2 Table

The next few slides will show you how to

calculate sensitivity and specificity. The gold

squares represent the 2x2 table, while the blue

boxes are labels. To understand the results from

the 2x2 table, we need information from the test

being evaluated and from the gold standard (or

reference test) results.

Slide 35: Sensitivity

To calculate sensitivity, or the proportion of

people with the disease who test positive, fill in

the squares of the 2x2 table with the numbers

with and without the disease who tested positive

or negative. People with the disease who test

positive are the true positives (TP). People with

the disease who test negative are the false

negatives (FN). People without the disease and who test positive are the false positives

(FP). People without the disease and testing negative are the true negatives (TN). To

calculate the sensitivity, divide the true positives by the total number with the disease,

i.e. TP / (TP+FN).

PSA level Sensitivity Specificity

1.0 100 21

2.0 100 48

3.0 100 60

4.0 99 73

5.0 96 76

6.0 94 79

7.0 90 83

8.0 90 88

9.0 68 90

10.0 54 93

11.0 47 94

12.0 30 95

13.0 23 96

14.0 17 97

15.0 11 97 Morgan TO et al; NEJM, 1996

PSA level Sensitivity Specificity

1.0 100 21

2.0 100 48

3.0 100 60

4.0 99 73

5.0 96 76

6.0 94 79

7.0 90 83

8.0 90 88

9.0 68 90

10.0 54 93

11.0 47 94

12.0 30 95

13.0 23 96

14.0 17 97

15.0 11 97 Morgan TO et al; NEJM, 1996

True Positive

Disease Present Disease Absent

Test +

Test -

False Positive

False Negative

True Negative

True Positive

Disease Present Disease Absent

Test +

Test -

False Positive

False Negative

True Negative

Sensitivity=

True positive False positive

False negative True negative

Present Absent

DISEASE

Test +

Test -

True positives

True positives + false negatives

Sensitivity

Sensitivity=



Present Absent

DISEASE

Test +

Test -

True positives

True positives + false negatives

Sensitivity

Module 4: Screening

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Page 14

Slide 36: Specificity

To calculate specificity, use the same 2x2 table,

and divide the true negatives by the total

number without the disease, i.e. TN / (FP+TN).

The specificity tells us the likelihood that test will

come back negative in someone without the

disease.

Slide 37: Predictive Values

Predictive value of a test is a measure of the

percentage of times the result (whether positive

or negative) is the correct result. The

percentage of all positive tests results that are

true positives is the positive predictive value.

The percentage of all negative test results that

are true negatives is the negative predictive

value. Predictive values are useful tools in clinical decision-making. They allow us to

determine the probability of the patient having a disease based on test results.

Slide 38: Positive Predictive Value (PPV)

PPV is not an inherent characteristic of a

screening test. PPV is affected by both the

specificity of the test and disease prevalence.

Specificity



Present Absent

DISEASE

Test +

Test -

= Specificity

True negatives

True negatives + false positives

Specificity



Present Absent

DISEASE

Test +

Test -

= Specificity

True negatives

True negatives + false positives

Positive predictive value

Negative predictive value

Positive predictive value

Negative predictive value

NOT inherent characteristic of a screening test

Percent of positive tests that are truly positive

If test result is positive, what is probability that the patient has the disease?

Is affected by several factors

Specificity & specificity of the screening test

Prevalence of disease


Percent of positive tests that are truly positive

If test result is positive, what is probability that the patient has the disease?

Is affected by several factors

Specificity & specificity of the screening test

Prevalence of disease

Module 4: Screening

TRANSCRIPT

Page 15

Slide 39: Negative Predictive Value (NPV)

NPV is also not an inherent characteristic of a

screening test. NPV is also affected by disease

prevalence. The NPV can tell us the probability

that the patient is disease-free based on

negative results.

Slide 40: Test Characteristics and Population

Tested

Sensitivity and specificity are constant for a

particular test, but it’s surprising and counter-

intuitive how dramatically the PPV and NPV vary

depending on the prevalence of the condition in

the specific population being tested. In a group

with low prevalence, a test will have a low PPV

and a high NPV. In a group with high prevalence, a test will have a high PPV and low

NPV.

Slide 41: Predictive Value and Prevalence

Here is a visual example of the relationship

between predictive values and prevalence.


Percent of negative tests that are truly negative

If test result is negative, what is the probability that patient does not have the disease?


Percent of negative tests that are truly negative

If test result is negative, what is the probability that patient does not have the disease?

Sensitivity and specificity are constant for a particular test

PPV and NPV vary dramatically, depending on prevalence of target condition in population tested

Low prevalence low PPV, high NPV

High prevalence high PPV, low NPV

Sensitivity and specificity are constant for a particular test

PPV and NPV vary dramatically, depending on prevalence of target condition in population tested

Low prevalence low PPV, high NPV

High prevalence high PPV, low NPV

0%

20%

40%

60%

80%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

PVPPVN

Prevalence

Pre

dic

tive

Va

lue

0%

20%

40%

60%

80%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

PVPPVN

Prevalence

Pre

dic

tive

Va

lue

Module 4: Screening

TRANSCRIPT

Page 16

Slide 42: Predictive Values

Now that we have done the basic 2x2 tables, let’s

figure out how to calculate PPV.

Slide 43: Positive Predictive Value

Let’s try some sample calculations to give you a

feel for how this works, using the ELISA test to

screen for HIV. The test’s sensitivity and

specificity are both over 90%. Let’s start with a

population with low prevalence – only 1.5% -- for

instance, a population of 1,000 patients at a

prenatal clinic. Using the ELISA in this population

gives us a positive predictive value of 12% and a negative predictive value of 99.9%.

Even among the patients who test positive, the probability that they have HIV is low. Put

another way, the probability that these patients got false positive results and are not

HIV-infected is quite high.


Now let’s look at a population with a high

prevalence of HIV. Here we have a population of

1,000 patients at an STD clinic. The HIV

prevalence is 6%. Using the same ELISA test, the

positive predictive value is 37%, much higher

than the neonatal clinic population. The NPV

remains high at 99.6%.

HIV Status

1,000 people at Prenatal Clinic

HIV-Positive (15) HIV-Negative (985) 1.5% Prevalence

ELISA Result

Positive True Positive (14) False Positive (99)

14

14 + 99

= 12.4% PPV

Negative False Negative (1) True Negative (886)

886

1 + 886

= 99.9% NPV

Sensitivity (95%) Specificity (90%)

HIV Status

1,000 people at Prenatal Clinic

HIV-Positive (15) HIV-Negative (985) 1.5% Prevalence

ELISA Result


14

14 + 99

= 12.4% PPV


886

1 + 886

= 99.9% NPV


HIV Status

1,000 people at STD Clinic

HIV-Positive (60) HIV-Negative (940) 6% Prevalence

ELISA Result


57

57 + 94

= 37.75% PPV


846

3 + 846

= 99.6% NPV


HIV Status

1,000 people at STD Clinic


ELISA Result


57

57 + 94

= 37.75% PPV


846

3 + 846

= 99.6% NPV


Module 4: Screening

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Page 17


Moving to a setting with a very high HIV

prevalence, for example in Zambia, has the

opposite effect. The PPV rises to 75%, and the

NPV falls slightly to 98.3%. The probability that

these test-positive Zambian patients have HIV is

quite high.

Slide 46: Multiple Screening Tests

Sometimes, it is prudent to use a series of tests

to screen for a condition. There may be no gold

standard screening tool available for a condition.

The available tools may be too invasive, costly,

or otherwise impractical to use for an initial

screening. We may use multiple screening tests

simultaneously or sequentially. Let’s take

screening for the presence of Down syndrome in a fetus. A common approach is to

simultaneously test for three key bio-markers in the mother’s blood. Each of these tests

individually has low sensitivity and specificity. Together, however, they provide a viable

alternative to amniocentesis. Amniocentesis is a highly sensitive and specific test.

However, it is also invasive and has a small but significant chance of causing a

miscarriage. It is better suited as a follow-up diagnostic test than a widespread screening

test.


Gestational diabetes testing generally employs a

two-stage screening protocol. In the first

trimester, a risk assessment is done to identify

women at risk for the condition. The Oral

Glucose Tolerance Test (OGTT) is then done for

women identified as at risk. This two-stage

protocol minimizes the number of women who

need the Oral Glucose Tolerance Test. The OGTT is a time-consuming test. Women must

stay at the clinic or lab for several hours. Most women’s risk of diabetes is low early in

pregnancy. Women who are obese or have a prior history of gestational diabetes need to

be screened earlier in pregnancy using the OGTT.

HIV Status

1,000 people at Clinic in Zambia


ELISA Result


228

228 + 76

= 75% PPV


684

12 + 684

= 98.3% NPV


HIV Status

1,000 people at Clinic in Zambia


ELISA Result


228

228 + 76

= 75% PPV


684

12 + 684

= 98.3% NPV


Use of different tests concurrently to screen for same condition

Example: Prenatal multiple marker screening for Down Syndrome

Measures levels of 3 biomarkers in mother’s blood:

▪ AFP: alpha-fetoprotein, protein produced by fetus

▪ hCG: human chorionic gonadotropin, hormone produced by placenta

▪ Estriol: a hormone produced by both fetus and placenta

Results of ALL 3 tests increases sensitivity and specificity

Use of different tests concurrently to screen for same condition

Example: Prenatal multiple marker screening for Down Syndrome

Measures levels of 3 biomarkers in mother’s blood:

▪ AFP: alpha-fetoprotein, protein produced by fetus

▪ hCG: human chorionic gonadotropin, hormone produced by placenta

▪ Estriol: a hormone produced by both fetus and placenta

Results of ALL 3 tests increases sensitivity and specificity

Use of two-stage screening to target testing efforts

Example: Early pregnancy gestational diabetes screening

First trimester risk assessment—identifies women at higher risk of gestational diabetes

Oral Glucose Tolerance Test (OGTT) right away for those whose first screen indicates high risk

Use of two-stage screening to target testing efforts

Example: Early pregnancy gestational diabetes screening

First trimester risk assessment—identifies women at higher risk of gestational diabetes

Oral Glucose Tolerance Test (OGTT) right away for those whose first screen indicates high risk

Module 4: Screening

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Page 18


Another use for two-stage screening is designed

to maximize predictive values. Let’s take an

example of HIV screening in a suburban primary

care office. A risk assessment about sexual and

drug use history is given to patients. Those with

risk factors for HIV infection are then given a

blood test. By using the written questionnaire as

a preliminary screening test and selecting the higher risk population to receive the blood

test, the number of false positive results is reduced, and the PPV of the test is increased.

These two examples of sequential screening tests illustrate different benefits of

sequential screening. Reducing the need for more invasive screenings and increasing the

PPV are just two.

Slide 49: Effectiveness of Screening Programs

The next few slides discuss effectiveness of

screening programs.

Slide 50: Screening Effectiveness Evaluation

Sensitivity and specificity alone are not sufficient

to make a sound clinical decision about whether

or not to use a screening test. We need to weigh

other factors in terms of the individual patient,

the healthcare system, and for society. We need

to analyze whether the benefits outweigh the

risks. We saw that amniocentesis carries

significant risks and should be used only when other tests indicate a need for more

intensive screening. Cancer screening in very old adults with a short life expectancy has

lower benefit (and perhaps higher risks) than screening healthy younger people.

Likewise, evidence is mounting that mammograms for women in the 40-50 year old age

range provide limited benefits because the prevalence of breast cancer in that age group

is so low, and they carry potentially unacceptable risks of excess radiation exposure and

false positives leading to stress and unnecessary invasive procedures. The level of

inconvenience is another factor to consider. Is the screening conducted in a location that

the patient can easily get to? If the screening protocol necessitates a follow-up, such as

for the PPD or HIV test, will the patient be able to follow through?

Two-stage screening to maximize predictive value

Example: HIV screening in suburban primary care office

Risk assessment questionnaire about sexual and drug use history

HIV blood test for all patients whose questionnaire indicates risk factors for HIV infection

Two-stage screening to maximize predictive value

Example: HIV screening in suburban primary care office

Risk assessment questionnaire about sexual and drug use history

HIV blood test for all patients whose questionnaire indicates risk factors for HIV infection

Test characteristics (sensitivity & specificity) alone are never sufficient for a sound decision about whether to use a screening test

Other screening considerations

Benefits vs. risks

Prevalence of target condition

Inconvenience

Costs/resource expenditures

Patient values and cultural norms

Guyatt: 2009

Test characteristics (sensitivity & specificity) alone are never sufficient for a sound decision about whether to use a screening test

Other screening considerations

Benefits vs. risks

Prevalence of target condition

Inconvenience

Costs/resource expenditures

Patient values and cultural norms

Guyatt: 2009

Module 4: Screening

TRANSCRIPT

Page 19

We must also look at the overall cost and resource needs to conduct a screening. Will it be covered by insurance? Are healthcare providers available for the screening and any follow-up tests? Finally, does the test fit with patients’ values or cultural norms? If a population firmly believes in a non-medicalized pregnancy experience, pregnant women from this group will be unlikely to agree to an amniocentesis, even if one is indicated. Likewise, some traditional Latinas or Muslim women may not follow through with breast or cervical cancer screenings due to cultural or religious beliefs. These are but a few considerations in designing a screening program.

Slide 51: Study Design

To assess diagnostic or screening tests, studies

seek to expose operating properties or

characteristics of the test and assess how close a

match these properties are to a “gold standard”

diagnostic test. Researchers seek to determine

the power of the tool to differentiate between

those with and those without a target condition.

To study a screening test, we look at the test’s performance in a group of patients NOT

known to have the target condition, and compare it to the performance of a “gold

standard” test. Gold standard tests are tests that are considered to be the diagnostic

standard for the target condition. (If there is no current gold standard test, the

researchers may have to follow patients over time to determine who develops

symptomatic disease.) The results of both tests are compared. In evaluating these

studies, we want to see one of two things. We want to see a great deal of similarity in

results between the two tests. Or, we want to see that the test in consideration exceeds

the capacity of the gold standard test to discriminate between presence and absence of

the condition. For example, we might ask about the test performance of the liquid-

based pap for cervical cancer screening. A group of women with no indication of cervical

cancer would be offered both the liquid-based pap and standard Pap smear. The rate of

positive, false positive, negative and false negative results would be compared for both

the liquid and standard Pap smear screens.

Slide 52: US Preventive Services Task Force

The US Preventive Services Task Force (USPSTF)

produces thoroughly researched screening

recommendations. Let’s spend a few minutes

talking about the USPSTF and how it works.

Assessing a screening/diagnostic test

Properties & accuracy

Comparison of test to “gold standard”

Most definitive diagnostic procedure or best available laboratory test

Not always a gold standard for a procedure

USPSTF recommended

Assessing a screening/diagnostic test

Properties & accuracy

Comparison of test to “gold standard”

Most definitive diagnostic procedure or best available laboratory test

Not always a gold standard for a procedure

USPSTF recommended

Module 4: Screening

TRANSCRIPT

Page 20

Slide 53: USPSTF Activities

The USPSTF is charged with systematically

reviewing the evidence of effectiveness and

developing recommendations for clinical

preventive services. The recommendations span

screening tests, counseling, and preventive

medications.

Slide 54: USPSTF Methodology

The USPSTF uses a rigorous methodology. First

the analytic framework is defined, including the

desired outcomes and key questions to be asked.

What constitutes relevant evidence is

operationally defined. The evidence is then

gathered. The overall quality of each of these

studies is evaluated individually. The evidence is

then synthesized and judged in aggregate. We want to see convincing or adequate

evidence at the very least. After this, the Task Force determines the balance of benefits

and harms, based on the evidence. From all of this information, a grade is assigned that

links the recommendations to judgments about the net benefits. Grades may range from

A to D, or an I may be assigned for inadequate evidence.

Slide 55: Critical Appraisal Questions

In evaluating the available evidence, the Task

Force asks a number of questions. Do the studies

have the appropriate research design to answer

key questions? Are the existing studies of high

quality? Finally, are the study results applicable

to the general primary care population and

setting?

Systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services

Recommendations include: Screening tests Counseling Preventive medications

Courtesy of Diana Pettiti, USPSTF: 2010

Systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services

Recommendations include: Screening tests Counseling Preventive medications


1. Define analytic framework – outcomes & questions

2. Define and retrieve relevant evidence

3. Evaluate QUALITY of studies (good, fair, poor)

4. Synthesize and judge STRENGTH of overall evidence (convincing, adequate, inadequate)

5. Determine BALANCE of benefits and harms Benefits – Harms = Net Benefit

6. Link recommendation to judgment about net benefits: Grades: A, B, C, D, I (inadequate evidence)


1. Define analytic framework – outcomes & questions

2. Define and retrieve relevant evidence

3. Evaluate QUALITY of studies (good, fair, poor)

4. Synthesize and judge STRENGTH of overall evidence (convincing, adequate, inadequate)

5. Determine BALANCE of benefits and harms Benefits – Harms = Net Benefit

6. Link recommendation to judgment about net benefits: Grades: A, B, C, D, I (inadequate evidence)


Do the studies have the appropriate research design to answer key questions?

Are the existing studies high quality?

Are the results of the studies applicable to the general US primary care population and setting?


Do the studies have the appropriate research design to answer key questions?

Are the existing studies high quality?

Are the results of the studies applicable to the general US primary care population and setting?


Module 4: Screening

TRANSCRIPT

Page 21

Slide 56: Critical Appraisal Questions

The number of studies that have been done is

evaluated, as well as the size of the studies. The

Task Force assesses the consistency of the

studies’ results. Finally, any other factors that

can help assess the certainty of the evidence are

weighed.

Slide 57: Interpret Task Force Grading

This slide shows us how to interpret the Task

Force grading system based on the magnitude of

net benefit. The task force uses letter grades for

their recommendations.

Slide 58: Communicating USPSTF

Recommendations

Here we see the letter grades defined, along with

suggested clinical practices.

How many relevant studies have been done?

How large are the studies?

How consistent are the results of the studies?

Are there other factors that help us assess the certainty of the evidence? (e.g. dose-response effects, biologic plausibility)


How many relevant studies have been done?

How large are the studies?

How consistent are the results of the studies?

Are there other factors that help us assess the certainty of the evidence? (e.g. dose-response effects, biologic plausibility)


Certainty of Net Benefit

Magnitude of Net Benefit

Substantial Moderate Small Zero/negative

High A B C D

Moderate B B C D

Low Insufficient (I Statement)


Certainty of Net Benefit

Magnitude of Net Benefit

Substantial Moderate Small Zero/negative

High A B C D

Moderate B B C D

Low Insufficient (I Statement)


Grade Grade Definition Suggestion for Practice

A USPSTF recommends the service.

There is high certainty that the net benefit is substantial. Offer or provide this service.

B

The USPSTF recommends the service.There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.

Offer or provide this service.

C

USPSTF recommends against routinely providing the service. There may be considerations that support providing

the service in an individual patient.There is moderate or high certainty that the net benefit is small.

Offer or provide this service only if there are other considerations in support of the offering or providing the service in an individual patient.

D

USPSTF recommends against the service.There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

Discourage the use of this service.

I

USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of

the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.

Read “Clinical Considerations” section of USPSTF Recommendation Statement. If offered the service, patients should understand the uncertainty about the balance of benefits and harms.


Grade Grade Definition Suggestion for Practice

A USPSTF recommends the service.

There is high certainty that the net benefit is substantial. Offer or provide this service.

B

The USPSTF recommends the service.There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.

Offer or provide this service.

C

USPSTF recommends against routinely providing the service. There may be considerations that support providing

the service in an individual patient.There is moderate or high certainty that the net benefit is small.

Offer or provide this service only if there are other considerations in support of the offering or providing the service in an individual patient.

D

USPSTF recommends against the service.There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

Discourage the use of this service.

I

USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of

the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.

Read “Clinical Considerations” section of USPSTF Recommendation Statement. If offered the service, patients should understand the uncertainty about the balance of benefits and harms.


Module 4: Screening

TRANSCRIPT

Page 22

Slide 59: Comparison of Screening Tools

Sometimes, there is only one effective test to

screen for a condition. However, often we have

choices, such as whether to use a newer test or

the existing gold standard. It’s important to

assess what are the best tests for the target

population. Tests should be valid for your

population. A test should have been normed for

the population you are working with. Tests should be accessible. This means that tests

should be covered under health insurance, and affordable. When we talk about

accessibility, we look at other issues, like language barriers and overall literacy. We also

look at privacy issues, particularly with tests that elicit sensitive information that could

stigmatize a patient if the information leaked out. The healthcare system must be able

to support use of a screening test or program. If we screen for colorectal cancer using the

FOBT, we need to ensure there is a colonoscopy provider in the area for follow-up

testing. If we recommend colonoscopy as the primary screen, we need to have many

more colonoscopists available. We also need to ensure that there are sufficient

resources for follow-up treatment. We ask where patients will get follow-up care,

whether they can get there, and if the care is affordable to them. In sum, there must be a

system in place that can deal with positive results.

Slide 60: Testing a Test

This diagram illustrates one way to test a

screening tool. We start out with patients

without any evidence of a target condition. In

this case, let’s use the example of cervical

cancer. We will compare a relatively new test;

the liquid based Pap smear, with our gold

standard, the standard Pap smear. We then

calculate the specificity and sensitivity of both tests. It’s quite important to start with

patients showing no evidence of the target condition. The sensitivity and specificity

characteristics of the test could be different in asymptomatic vs. symptomatic patients.

Screening tests are meant to be used on asymptomatic patients.

Newer tests vs. gold standard

Best tests for your population

Validity in your population

Accessibility

Cost

Capacity of local health care system

Need a system in place to be able to screen AND to deal with positive results

Newer tests vs. gold standard

Best tests for your population

Validity in your population

Accessibility

Cost

Capacity of local health care system

Need a system in place to be able to screen AND to deal with positive results

Liquid-basedPap smear –

the NEW testPatients withoutevidence of cervical cancer

NOCervical Cancer

NOCervical Cancer

Cervical Cancer

Cervical CancerStandardPap smear –the GOLD STANDARD

Liquid-basedPap smear –

the NEW testPatients withoutevidence of cervical cancer

NOCervical Cancer

NOCervical Cancer

Cervical Cancer

Cervical CancerStandardPap smear –the GOLD STANDARD

Module 4: Screening

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Page 23

Slide 61: Evaluating Screening Research

The only way to practice evidence-based

medicine (EBM) is to read the medical literature.

You will find some resources at the end of this

module on reliable sources of EBM literature.

The first question we always want to ask as we

read study results is whether the results are

credible. Look for the following information to

assess how valid the results were:

• Did the researcher enroll the right group of people? To test a screening test, the right group would comprise individuals without overt symptoms of the target condition

• Was the study sample large enough to draw conclusions? • Were the methods employed to test the screen appropriate to the study aims? • Did all the subjects get both the target AND gold standard test? • Some diseases necessitate re-screening for inconclusive results or to allow the

disease time to be visible to screening tools. For the target condition, was enough time allowed to lapse between re-screenings where appropriate?

Next we evaluate what the researchers say about specificity, sensitivity and predictive value.

• Do the authors convey the importance of classifying patients correctly and the implications of false negatives and false positives?

• Is the predictive value calculated in a population whose disease prevalence is similar to the target patient population?

If the results are valid and sufficiently large and stable, then we look to apply what we’ve learned.

• Who would this screen likely work for? Who might it not work for? Who has it not been “normed” for? For this, we need to know who was represented in this and other studies.

• Also, what would be the net impact of the screening? For example, what are the benefits and any likely side effects or adverse reactions?

• How does the test improve on the current state of preventive medicine? We want to see a test that will enhance accuracy or make screening easier, more accessible, or cheaper. The test should make a positive contribution to medicine and patient care. This may be through more accurate results, reduced cost, diminished pain and intrusiveness, or perhaps less time taken to complete the test.

1. Are study methodology and results credible?

2. Have sensitivity, specificity and predictive values been calculated and reported?

3. Is the population tested similar to my patient population?

4. How can I use these results in a screening program or patient care?

5. Does this screening improve the present state of medical screening?

1. Are study methodology and results credible?

2. Have sensitivity, specificity and predictive values been calculated and reported?

3. Is the population tested similar to my patient population?

4. How can I use these results in a screening program or patient care?

5. Does this screening improve the present state of medical screening?

Module 4: Screening

TRANSCRIPT

Page 24

Slide 62: Screening Outcome Considerations

We need to be cautious about inferring survival

rates from screening detected cases alone. There

are inherent biases in screen-detected long-term

disease outcomes. By screening, we seek to

diagnose a disease earlier than it would be found

without screening. Without screening, the

disease may be discovered later, when

symptoms appear. Let’s compare two cases in which a person is diagnosed with uterine

cancer. Even if both patients die at the same time, because we diagnosed the cancer

early with screening, the survival time after diagnosis is longer with screening. Life has

not been extended for the patient who was screened. In fact, the patient who was

diagnosed earlier may suffer added emotional effects from living with the knowledge of

a potentially terminal diagnosis for longer. If we examine only the raw numbers,

screening appears to increase survival time, even though all that has really happened is

an earlier diagnosis. This is called lead time bias. Length bias is more subtle than lead

time bias. Using uterine cancer again as an example, if we conduct regular screenings for

uterine cancer, the chances are excellent that we will pick up many slow-growing

cancers. In fact, we will pick up more slower-growing tumors than fast ones. Rapidly

growing tumors have shorter asymptomatic phases where they could be found through

screening and lower survival rates. Again, if we look at raw numbers, we might

incorrectly deduce that people whose cancer is detected by screening live longer, when

in fact, the screening has just picked up a disproportionate number of slow-growing

cancers.

Slide 63: To Screen or Not to Screen

This table provides criteria for when to screen

Lead time bias: over-estimation of survival rate among screening-detected cases

When survival is calculated from diagnosis point

Length bias: over-estimation of survival rate among screening-detected cases

Due to excess of slowly progressing cases among those identified by screening

Koretz: 2009

Lead time bias: over-estimation of survival rate among screening-detected cases

When survival is calculated from diagnosis point

Length bias: over-estimation of survival rate among screening-detected cases

Due to excess of slowly progressing cases among those identified by screening

Koretz: 2009

Disease Test Treatment Cost ProgrammingConditionshould be important health problem.

Test must be simple, safe, precise, valid.

Must be evidence ofeffective treatment and that early treatment will lead to better outcomes.

Evidence on cost-effectiveness of screening for interventions and outcomes.

Evidence from randomized controlled trials that program effective in reducing mortality and morbidity.

Epidemiology of disease must be understood.

Must be acceptable to population andhealth providers giving test.

Benefits outweigh physical and psychological harms if any.

Criteria/protocol on next steps forpositive tests.

Protocols forimplementation and evaluation of screening program.

Disease Test Treatment Cost ProgrammingConditionshould be important health problem.

Test must be simple, safe, precise, valid.

Must be evidence ofeffective treatment and that early treatment will lead to better outcomes.

Evidence on cost-effectiveness of screening for interventions and outcomes.

Evidence from randomized controlled trials that program effective in reducing mortality and morbidity.

Epidemiology of disease must be understood.

Must be acceptable to population andhealth providers giving test.

Benefits outweigh physical and psychological harms if any.

Criteria/protocol on next steps forpositive tests.

Protocols forimplementation and evaluation of screening program.

Module 4: Screening

TRANSCRIPT

Page 25

Slide 64: Pseudodisease

Pseudo disease or over-diagnosis is defined as

the identification of disease that would be

unlikely to impact the patient during their

lifetime. This is the major concern with both

mammography and prostate screening. We may

find histologic evidence of cancer, but we’re

often picking up a lot of “cancer” of little clinical

importance. Even a gold standard “diagnostic” test isn’t a perfect window on the future.

As a result of screening, some individuals will be diagnosed and treated for an illness that

would never have become clinically apparent.

Slide 65: Screening and Ethics

Next, we will discuss just a few of the ethical

considerations around screening.

Slide 66: Ethical Considerations

We will discuss mandatory screening programs,

genetic testing, and health disparities around

screening. Finally, we will talk about

considerations in creation of a screening

program.

Definition: Identifying a disease that is unlikely to impact patient over lifetime

Prostate or breast cancer may be present in body

May never become clinically apparent

Identifying pseudodisease is nearly impossible until person dies from unrelated causes

Gold standard tests cannot predict future trajectory of a condition

Durgin: 2005

Definition: Identifying a disease that is unlikely to impact patient over lifetime

Prostate or breast cancer may be present in body

May never become clinically apparent

Identifying pseudodisease is nearly impossible until person dies from unrelated causes

Gold standard tests cannot predict future trajectory of a condition

Durgin: 2005

Mandated screening

Genetic testing

Disparities

Creation of screening program

Mandated screening

Genetic testing

Disparities

Creation of screening program

Module 4: Screening

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Page 26

Slide 67: Mandatory Screening

There are more mandated screening programs

affecting Americans today than we might realize.

Every person applying for a marriage license

must take a blood test for syphilis. All healthcare

workers are tested for tuberculosis. Drug testing

is mandated for airline pilots. We discussed

newborn screening earlier. Each of these

screening protocols has an important role in public health. Yet, there will always be

concerns around universal testing. We will get into a few of these.


We need to do a cost-benefit analysis at all levels

from the individual all the way to the societal

costs and benefits. We must ensure that the

benefits outweigh any costs. Let’s take the

example of doing drug screens in airline pilots.

The benefits are clear. We may avoid airline

accidents caused by drug-impaired pilots

operating aircrafts. This potentially saves hundreds, even thousands, of lives. The costs of

testing include inconvenience of testing or possible flight cancellation if a pilot tests

positive. However, the costs are outweighed by the benefits to society.


The benefits to mandated testing are often clear.

We can identify serious problems that can harm

others. We also identify conditions necessitating

immediate treatment.

The costs may not be so clear at times, but every decision has potential consequences. Patients undergoing mandatory screening lose their

autonomy. We may not be able to maintain confidentiality in certain situations, such as diagnosis of syphilis or HIV/AIDS testing. If we are testing a low risk population, the positive predictive value is decreased and the consequences of false positives are increased.

Newborn screening

Syphilis testing for marriage licenses

TB screening for health care workers

Drug testing for airline pilots

Newborn screening

Syphilis testing for marriage licenses

TB screening for health care workers

Drug testing for airline pilots

Need to assess costs vs. benefits at all levels

Individual

Societal

Healthcare system

Need to assess costs vs. benefits at all levels

Individual

Societal

Healthcare system

Pros

Identify serious problems that could harm others OR where immediate treatment is imperative

Cons

Potential harm to patient autonomy

Confidentiality concerns

Testing low risk population reduces PPV

Consequences of false positive tests

Pros

Identify serious problems that could harm others OR where immediate treatment is imperative

Cons

Potential harm to patient autonomy

Confidentiality concerns

Testing low risk population reduces PPV

Consequences of false positive tests

Module 4: Screening

TRANSCRIPT

Page 27

Slide 70: Genetics Testing

Genetic testing has many benefits. Chief among

them is screening for disease that can affect not

only the individual tested, but also other

members of his or her family. Individuals can be

tested to see if they carry genes for diseases that

may be passed on to children. An example would

be Fragile X Syndrome, a developmental

disability. Unborn children can be screened for diseases, such as Down syndrome.

Genetic diseases can be identified in people of all ages before symptoms become

evident.

Slide 71: Genetic Testing

Results of genetic testing must be interpreted

carefully by a trained medical geneticist or a

genetic counselor. A positive result in genetic

testing does not necessarily mean that the

person will develop the disease. With these

results come decisions—often difficult ones.

Should someone with a genetic marker for

ovarian cancer have their ovaries removed proactively? Likewise, if a fetus tests positive

in utero for Down syndrome, will the couple have the baby or abort? While a negative

result most often brings peace of mind, a positive result can trigger enormous stress.

Take the decision to have pre-emptive surgery, such as ovary removal, to avoid cancer.

These are difficult decisions and lead to major life changes. Proper genetic testing must

be done through a medical provider. At-home genetic testing kits are generally not

effective, except for a very few approved by the FDA. However, some people turn to

them due to high costs, lack of insurance coverage for testing, privacy concerns, or

aggressive advertising. Genetic testing may bring up confidentiality issues. A breach in

confidentiality can lead to risk of job loss, difficulties maintaining health insurance, and

difficulty obtaining a life insurance policy. Recent federal legislation forbids use of

genetic test results in these settings, but a person might have to defend those rights in

court. A final ethical issue with genetic testing involves the ownership of the DNA. When

DNA goes to a laboratory for testing, many laboratories will keep the DNA for further

testing. They retain proprietary rights to a person’s genetic material. For some patients,

this is not a major concern, but for many it will be. It’s important to know the policies of

any genetic testing facility and to be sure that patients are fully informed, as well.

Learn if individual carries a gene for a disease and might pass it on to children

Screen unborn fetus for disease

Test for genetic diseases in children or adults before symptoms emerge

Learn if individual carries a gene for a disease and might pass it on to children

Screen unborn fetus for disease

Test for genetic diseases in children or adults before symptoms emerge

Results difficult to interpret; not always clear cut

Employment issues

Health/life insurance consequences

Added stress

Costs

Confidentiality

Ownership of DNA

Kalb, 2006

Results difficult to interpret; not always clear cut

Employment issues

Health/life insurance consequences

Added stress

Costs

Confidentiality

Ownership of DNA

Kalb, 2006

Module 4: Screening

TRANSCRIPT

Page 28

Slide 72: Disparities

Rural areas often lack access to local healthcare.

Additionally, many people struggle with

transportation to reach healthcare providers.

Rural areas tend to have sparse public

transportation, if any. Hospital closures in rural

areas are on the rise in many states. Hospital-

based screenings become more difficult to

obtain in these areas. Inner cities have similar challenges in terms of limited resources,

though fewer transportation issues. People who lack insurance or are under-insured

often have great difficulty receiving health screening. Affordability of screening is a huge

issue for the uninsured, as is education on which screening tests are most critical to

obtain. Many uninsured individuals do not have primary care doctors, depriving them of

crucial advice about screenings. In addition, they receive much of their healthcare in

emergency room settings, which are not designed to provide preventive care. Migrant

and immigrant populations often face serious barriers to health care, including screening.

Migrant farm workers are among the most economically disadvantaged and medically

vulnerable groups in the US. They have little or no access to health care or medication.

Barriers may include lack of health insurance, language barriers, lack of transportation,

fear of deportation, and lost income. Migrant workers also face the very real threat of

being fired or not invited back to work because of health issues or time lost due to

medical appointments. With such insurmountable barriers, migrant workers are not

likely to risk their incomes for health screening. What can minimize some of these

barriers? Mobile screening units may improve access to screenings. Many of these

mobile units offer free or low-cost screening tests. This may necessitate use of non-gold

standard screening tests. Non-gold standard tests may be more affordable and easier to

administer in a mobile unit. They may also require fewer follow-up tests or procedures.

Additionally, after-hours screening options may be a viable alternative for migrant farm

workers. Bi-lingual health educational initiatives may also help improve access to

screening.

Geographic region

Rural

Inner city

Uninsured and underinsured

Screening and follow-up testing/treatment

Cost-prohibitive without health insurance

Minority and immigrant populations

Lack of culturally competent healthcare providers

Low health literacy

Geographic region

Rural

Inner city

Uninsured and underinsured

Screening and follow-up testing/treatment

Cost-prohibitive without health insurance

Minority and immigrant populations

Lack of culturally competent healthcare providers

Low health literacy

Module 4: Screening

TRANSCRIPT

Page 29

Slide 73: Disparities

Information about diseases, prevention and

screening practices, is disseminated differentially

across cultures. For example, not all groups

receive culturally sensitive education on

screening and preventive health in general. We

often see a lack of detailed information provided

to non-English speaking patients. Patients from

certain cultures may have specific world views of illnesses. For example, in some Asian

and Hispanic cultures, a cancer diagnosis may be viewed with a sense of fatalism. There

is a growing evidence base on best practices for adapting education, outreach, and

screening protocols to be more culturally sensitive. For example, if we look at prostate

cancer, African American groups might do better with outreach that details the risk

factors for prostate cancer, the benefits of being screened, and ways to get screened.

Mexican males, on the other hand, receive the least amount of health information of all

ethnic groups researched in the US. An increase in health education outreach to this

group is of vital importance. Screening practices often need to be adapted, depending

on the target group. For example, an Iraqi woman may have great difficulty accepting

screening for breast or uterine cancer from a male doctor, despite having a female nurse

in the room. Likewise, having medical students in the room during a Pap smear might

lead to future avoidance of these screenings. Services can be made much more sensitive

to the patient’s cultural background by a thorough explanation and an examination by a

female medical provider.

Slide 74: Developing a Screening Program

As we develop a screening program, we need to

address some ethical questions. First, how

ethical is it to use a test that may tell people they

have condition when they do not? If we embark

on this screening program, will those with false

positive test results engage in unnecessary

testing or invasive procedures? If they do, who

will pay for it? We need to examine the potential adverse effects to unnecessary testing.

We also need to consider the potential for emotional distress in patients screened false

positive? How ethical is it to use a test that may tell people they do not have condition

when they actually do? What happens to these people? How much later will they be

diagnosed, and how will this affect their mortality or morbidity? Again, we need to

consider the potential for emotional distress when they are finally diagnosed. Finally, we

need to consider the outcomes if we develop a screening program without a system in

place to treat those who test positive. What if we embark on an HIV/AIDS screening

program in a very remote Kenyan community 20 kilometers from the nearest hospital or

Cross-cultural differences in health literacy and attitudes

Culturally relevant screening

Screening practices may need to be adapted

Cross-cultural differences in health literacy and attitudes

Culturally relevant screening

Screening practices may need to be adapted

How ethical is it to:

Use a test that may tell people they have condition when they do not?

Use a test that may tell people they do not have condition when they actually do?

Use a test if there is no system in place to treat those who test positive?

Truglio et al: 2011

How ethical is it to:

Use a test that may tell people they have condition when they do not?

Use a test that may tell people they do not have condition when they actually do?

Use a test if there is no system in place to treat those who test positive?

Truglio et al: 2011

Module 4: Screening

TRANSCRIPT

Page 30

clinic? Those with positive ELISA results face nearly insurmountable barriers to accessing

follow-up diagnostic testing and care. Before screening can ethically be offered, we may

be faced with a daunting task of developing an infrastructure to provide treatment.

Slide 75: Implications for Practice

Strategic screening protocols can lead to

increased precision in screening for disease.

Identification of groups with higher prevalence

and targeting screenings toward these groups

will increase the test’s predictive value and

provide earlier intervention opportunities for

those identified as having the disease. Strategic

targeting also incorporates knowledge of whom to educate on the importance of a

particular screening. In some cases, education and outreach to patients is an efficient

method. However, in some cases, such as pap smears or mammograms, the doctor

often suggests these screens. In this case, the medical provider is an important target for

education and outreach. In some cultures, all medical decisions are made by elders in

the family, in which case their education is crucial. With shrinking resources and an aging

population, evidence based medicine is a valuable resource to identify more accurate

screening tools and protocols. Critical review of the literature provides a mechanism for

weighing the benefits and costs of particular screens for your patient population. As we

have discussed, the gold standard may not be best for your community or your practice.

Screening can be a cost-effective method of earlier disease identification and improved

treatment outcomes. It is important to keep up with accumulating evidence to

determine the best screening practices for your practice and community.

Slide 76: Summary

There are several key points to take away from

this module. Screening is the bedrock of

secondary prevention. Screening and diagnosis

are not the same thing. Screening is conducted

on asymptomatic patients, while diagnosis is

conducted on patients showing some signs or

symptoms of the target disease. Sensitivity and

specificity are characteristics of a screening test that determine a test’s validity.

Predictive values are affected by the sensitivity and specificity of the screening test and

by the prevalence of the target condition in the population. Targeting screening to high-

risk populations increases the positive predictive value. Decisions on screening protocols

must weigh the acceptability and applicability to the practitioner, population, and

individual patient.

Strategic targeting for screening

Groups with higher prevalence – increase PPV

Provider vs. patient – who is more likely to request?

Growing body of evidence-based medicine allows us to:

Identify more precise screening protocols

Weigh benefits/drawbacks of screening test

Strategic screening can be cost-effective

Strategic targeting for screening

Groups with higher prevalence – increase PPV

Provider vs. patient – who is more likely to request?

Growing body of evidence-based medicine allows us to:

Identify more precise screening protocols

Weigh benefits/drawbacks of screening test

Strategic screening can be cost-effective

Screening is bedrock of secondary prevention

Screening and diagnosis are not the same

Sensitivity and specificity are characteristics of a screening test that determine a test’s validity

Predictive values are affected by sensitivity & specificity of test and by prevalence of the disease

Screening of high-risk populations increases positive predictive value

Screening decisions must weigh acceptability and applicability to practitioner, population, andindividual

Screening is bedrock of secondary prevention

Screening and diagnosis are not the same

Sensitivity and specificity are characteristics of a screening test that determine a test’s validity

Predictive values are affected by sensitivity & specificity of test and by prevalence of the disease

Screening of high-risk populations increases positive predictive value

Screening decisions must weigh acceptability and applicability to practitioner, population, andindividual

Module 4: Screening

TRANSCRIPT

Page 31

Department of Public HealthBrody School of Medicine at East Carolina University

Department of Community & Family MedicineDuke University School of Medicine

Mike Barry, CAELorrie Basnight, MDNancy Bennett, MD, MSRuth Gaare Bernheim, JD, MPHAmber Berrian, MPHJames Cawley, MPH, PA-CJack Dillenberg, DDS, MPHKristine Gebbie, RN, DrPHAsim Jani, MD, MPH, FACP

Denise Koo, MD, MPHSuzanne Lazorick, MD, MPHRika Maeshiro, MD, MPHDan Mareck, MDSteve McCurdy, MD, MPHSusan M. Meyer, PhDSallie Rixey, MD, MEdNawraz Shawir, MBBS

Sharon Hull, MD, MPHPresident

Allison L. LewisExecutive Director

O. Kent Nordvig, MEd

Project Representative

Discuss ethical considerations in screening Cheryl Reeves, MS, MLS · 2018-04-01 · Slide 13: Screening versus Diagnostic Tests Diagnostic tests, on the other hand, are used to determine

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