Screening methods Dr K N Prasad Community Medicine.

Screening methods

Dr K N Prasad

Community Medicine

Diseases are having iceberg phenomenon

Screening is the early detection of disease precursors to disease. Or susceptibility to diseases in individuals who do not show any signs of the disease

TestsQuestions

Examinations

Laboratory tests

X rays

Definition: “The PRESUMPTIVE identification of UNRECOGNIZED disease or defect by the application of tests, exams or other procedures which can be applied RAPIDLY to sort out apparently well persons who PROBABLY have a disease from those who PROBABLY do not.”

Screening refers to the application of a medical procedure or test to people who as yet have no symptoms of a particular disease, for the purpose of determining their likelihood of having the disease.

The screening procedure itself does not diagnose the illness.

Screening test will need further evaluation with subsequent diagnostic tests or procedures.

Differences Screening test Done on apparently

healthy Applied to groups Based on one or cut off

criteria Less accurate Not a basis for treatment Initiative comes from the

health agency

Diagnostic test Done on those with sick

or indications Applied to single patient Based on evaluation of

number of symptoms, signs or lab tests

More accurate Basis for treatment Initiative comes from

patient with complaint

Lead time concept

• Time lag present between disease onset and usual time of diagnosis

Disease onset

First possible detection

Final critical point

Usual time ofdiagnosis outcome

Screening time

Lead time

A

B

Lead time is the period between diagnosis by early detection and diagnosis by other means

Screening pathwaysHealthy

Disease or precursorDetectable

Symptoms develop

Advance disease

Death

Screening possible

Intervention to avert disease development or its consequences

Life prolonged

Objective The goal of screening is to reduce morbidity or

mortality from the disease by detecting diseases in their earliest stages, when treatment is usually more successful.

Sort out the population who has risk from others

ExaminationsPap smear, Mammogram, Clinical breast exam, Blood

pressure determination, Cholesterol level, Eye examination/vision test, and Urinalysis.

Uses of screening tests1. Cases detection (Prescriptive )

1. Screened primarily for their own benefit Ex. Neonatal, cancers

2. Control of diseases (Prospective)1. Screened for benefit of others 2. Ex. STD, TB

3. Research purpose1. May aid in obtaining basic knowledge about

natural history of disease4. Education opportunity

1. To create public awareness and educating health professionals

Types of screening1. Mass screening

1. Screening afford to all irrespective of the particular risk Ex. TB

2. High risk or selection screening1. Applied to selective high risk group on the

basis of epidemiological research2. Ex. Cervical Cancer, heart diseases

3. Multi purpose screening1. Application of two or more tests in

combination to a large number at one time2. Ex. Questionnaire, examination, laboratory

tests etc.

Criteria for population based screening

1. Knowledge of disease1. Condition must be an important problem

2. Presence of recognisable latent or early symptomatic stage

3. Natural history of the condition must be adequately understood

2. Feasibility of screening procedures1. Suitable test or examination

2. Acceptable to the population

3. Should be a continuous process

Contd. Diagnosis and treatment acceptable treatment with recognisable

disease Facilities for diagnosis & treatment should be

available agreed upon policy to treat as patients

Cost considerations adequate resources Expected benefit

Principles 1. Condition should be an important public health

problem2. There should be a recognizable early or latent

stage3. There should be an accepted treatment for

persons with condition4. The screening test is valid, reliable and acceptable

yield5. The test should be acceptable to the population to

be screened6. The cost of screening and case finding should be

economically balanced in relation to medical care as a whole

Screening testsAcceptability :

Simple, minimum pain or discomfort, easy, safety, rapidity , acceptable procedure, etc.

RepeatabilityMust give consistent result when repeated

several times on the same subject or individual

Observer variationBiological variation

Observer variationIntra observer or within observer variation

Measurements should be same( subject or material) if recorded several times at that time or event

Ex. Ht, wt, lab tests. etc..

Inter observer variation or between observer variationDifferences in measurements on the same

( subject or material) by different investigatorsEx. X ray, blood smears, organisms, etc..

Biological variation1. Variation in physiological variables. Ex. BP,

Rates, etc.

2. Changes in parameters observed1. Ex. MI, Cancers, etc

3. Variations in their symptoms /signs1. Memory, pain, quality of care, etc.

4. Regression to the mean1. Tendency of values merge at the mean.

This is tested by repeated observation over time

Thought for the day

Every job is a self portrait of the person who did it.

Autograph your work with excellence.

Thank youThank you

Difference• Screening test is intended for initial

examination.

• Diagnosis involves confirmation of presence or absence of disease in someone suspected or at risk for having a disease.

• Case finding measures