CA Diagnostic KBK1

8/3/2019 CA Diagnostic KBK1

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Critical AppraisalCritical AppraisalOn Article of Diagnostic TestOn Article of Diagnostic Test

(EBM(EBM--Diagnostic)Diagnostic)


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Critical appraisal is one step in the process of evidence-based clinical practice.

To determine what is the best evidence, we need criticalappraisal skills that will help us to understand the

methods and results of research and to assess thequality of the research.

Most research is not perfect, and critical appraisal is notan exact science - it will not give us the right answer.But it can help us to decide whether we think areported piece of research is good enough to be usedin decision making.


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THREE MAIN ASPECTS TO BE APPRAISED:THREE MAIN ASPECTS TO BE APPRAISED: V I AV I A

1.1. VALIDITY :VALIDITY :

VALID (CLOSENESS TO THE TRUTH)VALID (CLOSENESS TO THE TRUTH) pp IN THEIN THEMETHODOLOGY SECTIONMETHODOLOGY SECTION

2.2. IMPORTANCE :IMPORTANCE :

IMPORTANT (USEFULNESS)IMPORTANT (USEFULNESS) pp IN THE RESULTS SECTIONIN THE RESULTS SECTION

3.3. APPLICABILITY :APPLICABILITY :

APPLICABLE (CAN BE APPLIED IN CLINICAL PRACTICE)APPLICABLE (CAN BE APPLIED IN CLINICAL PRACTICE) ppIN THE DISCUSSION SECTIONIN THE DISCUSSION SECTION


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DIAGNOSIS WORKSHEET

Citation:

Are the results of this diagnostic study valid?

Was there an independent, blind comparison with areference (gold) standard of diagnosis?

Was the diagnostic test evaluated in an appropriate

spectrum of patients (like those in whom it would be

used in practice)?Was the reference standard applied regardless of the

diagnostic test result?

Was the test (or cluster of tests) validated in a second,

independent group of patients?


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Are the valid results of this diagnostic study important?SAMPLE CALCULATIONS

Target disorder

(iron deficiency anemia)

Totals

Present Absent

Diagnostic

test result

(serum

ferritin)

Positive

(< 65 mmol/L)

731

a

270

b

1001

a+b

Negative

(u 65 mmol/L)

78

c

1500

d

1578

c+d

Totals 809

a+c

1770

b+d

2579

a+b+c+d

Sensitivity = a/(a+c) = 731/809 = 90%

Specificity = d/(b+d) = 1500/1770 = 85%

Likelihood ratio for a positive test result = LR+ = sens/(1-spec) = 90%/15% = 6Likelihood ratio for a negative test result = LR - = (1-sens)/spec = 10%/85% = 0.12

Positive Predictive Value = a/(a+b) = 731/1001 = 73%

Negative Predictive Value = d/(c+d) = 1500/1578 = 95%

Pre-test probability (prevalence) = (a+c)/(a+b+c+d) = 809/2579 = 32%Pre-test odds = prevalence/(1-prevalence) = 31%/69% = 0.45

Post-test odds = pre-test oddsv

LRPost-test probability = post-test odds/(post-test odds +1)


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YOUR CALCULATIONS

Target disorder

Totals

Present Absent

Diagnostic

test result

Positive a b a+b

Negative c d c+d

Totals a+c b+d a+b+c+d


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Can you apply this valid, important evidence about

a diagnostic test in caring for your patient?

Is the diagnostic test available, affordable, accurate, and precise in your

setting?

Can you generate a clinically sensible estimate of your patients pre-test

probability (from personal experience, prevalence statistics, practice

databases, or primary studies)?

yAre the study patients similar to your own?

yIs it unlikely that the disease possibilities or probabilities have changed

since the evidence was gathered?

Will the resulting post-test probabilities affect your management and help

your patient?

yCould it move you across a test-treatment threshold?yWould your patient be a willing partner in carrying it out?

Would the consequences of the test help your patient?

Additional notes:


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Bedside Diagnosis ofBedside Diagnosis of

Influenzavirus InfectionsInfluenzavirus Infections

in Hospitalized Childrenin Hospitalized Children

Katherine A. Poehling, et alKatherine A. Poehling, et al

American Academy of PediatricsAmerican Academy of Pediatrics

Example : an article of diagnostic test, entitle :Example : an article of diagnostic test, entitle :


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Background:Background:

Influenzavirus has a significant impact on the pediatricpopulation, with school-aged children having the highestinfection rates.

For preventing nosocomial influenza infections and tofacilitate prompt antiviral therapy, an accessible, rapid

diagnostic method for influenzavirus is needed.

Objective:Objective:

To compare the performance of a rapid diagnostic test

(QuickVue Influenza Test; Quidel Corp, San Diego, CA)completed at the bedside of hospitalized children to viralculture and/or polymerase chain reaction (PCR) forinfluenzavirus.


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Method:Method:

Study population:

1) younger than 19 years and hospitalized with respiratorysymptoms or 2) younger than 3 years and hospitalized with

fever. Sampel: 1) a primary admission diagnosis of an acute

respiratory illness characterized by rhinorrhea, sore throat,cough, shortness of breath, or apnea or 2) a primaryadmission diagnosis consistent with a febrile illness and a

temperature of 100.4F. Broad inclusion criteria were chosen such that all children

who were hospitalized with symptoms potentially related toinfluenza infections were eligible.


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Sample in

this study


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Study design:Study design:

prospective, cross sectional studyprospective, cross sectional study ffrom each child, 2 nasalswabs of the turbinates were obtained1 for influenzavirusculture and PCR and the other for the rapid diagnostic test.

The rapid test results were compared with that of culture andPCR for influenzavirus.

Influenza infection was defined as any sample with 1) apositive culture for influenzavirus or 2) 2 consecutive positivePCRs for influenza A or B.

Each researcher was trained to perform and interpret the

rapid diagnostic test at the bedside according to themanufacturers instructions.

The laboratory technician who performed the culture andPCR was masked to the rapid diagnostic test results.


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Results:Results:


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Sens: 74%

Spec: 98%PPV: 74%

NPV: 98%


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DIAGNOSIS WORKSHEET

Citation:

Are the results of this diagnostic study valid?

Was there an independent, blind comparison with areference (gold) standard of diagnosis?

YesYes

Was the diagnostic test evaluated in an appropriate

spectrum of patients (like those in whom it would be

used in practice)?

YesYes

Was the reference standard applied regardless of the

diagnostic test result?

YesYes

Was the test (or cluster of tests) validated in a second,

independent group of patients?

YesYes


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Are the valid results of this diagnostic study important?

SAMPLE CALCULATIONS

Target disorder

Totals

Present Absent

Diagnostic

test result

Positive a b a+b

Negative c d c+d

Totals a+c b+d a+b+c+d


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++ --

++ 1414 55

-- 55 209209


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Culture or PCR Totals

Present Absent

Quick VueInfluenza

test

Positive 14 5 19

Negative 5 209 214

Totals 19 214 233

Sensitivity = a/(a+c) = 14/19 = 74%

Specificity = d/(b+d) = 209/214 =98%

Likelihood ratio for a positive test result = LR+ = sens/(1-spec) = 74%/2% = 37

Likelihood ratio for a negative test result = LR - = (1-sens)/spec = 26%/98% = 0.27

Positive Predictive Value = a/(a+b) = 14/19 = 74%Negative Predictive Value = d/(c+d) = 209/214 = 98%

Pre-test probability (prevalence) = (a+c)/(a+b+c+d) = 19/233 = 8%

Pre-test odds = prevalence/(1-prevalence) = 8%/92% = 0.087

Post-test odds = pre-test odds v LR = 0.087 x 37 = 3.22

Post-test probability = post-test odds/(post-test odds +1)= 3.22/4.22=76%


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Just to remind you:Just to remind you:

Sensitivity: the percentage of persons with theSensitivity: the percentage of persons with the

disease of interest who have positive test results.disease of interest who have positive test results.

=a/(a+c) x 100

=a/(a+c) x 100

Specificity: the percentage of persons withoutSpecificity: the percentage of persons without

the disease of interest who have negative results.the disease of interest who have negative results.= d/(d+b) x 100= d/(d+b) x 100


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PPV: the percentage of persons with positivePPV: the percentage of persons with positivetest results who actually have the disease oftest results who actually have the disease ofinterest.interest.

= a/(a+b) x 100= a/(a+b) x 100

NPV: the percentage of persons with negativeNPV: the percentage of persons with negative

test results who do not have the disease oftest results who do not have the disease ofinterest.interest.

= d/(d+c) x 100= d/(d+c) x 100


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Likelihood RatioLikelihood Ratio

Likelihood is the probability of a particular testLikelihood is the probability of a particular test

result for a person with the disease of interestresult for a person with the disease of interest

divided by the probability of that test result for adivided by the probability of that test result for a

person without the disease of interest.person without the disease of interest.

Likelihood Ratio for a positive test result (LRLikelihood Ratio for a positive test result (LR++))

Likelihood Ratio for a negative test result (LRLikelihood Ratio for a negative test result (LR--))


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(LR(LR++) is the probability of a positive test result for a) is the probability of a positive test result for aperson with the disease of interest divided by theperson with the disease of interest divided by the

probability of a positive test result for a person withoutprobability of a positive test result for a person withoutthe disease.the disease.

LRLR++ =Sensitivity / (1=Sensitivity / (1--Specificity)Specificity)

LRLR

++

> 1:> 1: persons affected with disease of interest arepersons affected with disease of interest aremore likely to have a positive test result than unaffectedmore likely to have a positive test result than unaffectedpersons.persons.

The larger the value of the LR, the stronger theThe larger the value of the LR, the stronger theassociation between having a positive test result andassociation between having a positive test result and

having the disease of interest.having the disease of interest. LRLR++value of 10 or greater is perceived as indication ofvalue of 10 or greater is perceived as indication of

a test of high diagnostic value.a test of high diagnostic value.


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Pretest probability of diseasePretest probability of disease: the probability that a: the probability that a

person has the disease of interest before the test isperson has the disease of interest before the test isperformed.performed.

= prevalence= prevalence

Pretest odds of diseasePretest odds of disease: the estimate before diagnostic: the estimate before diagnostictesting of the probability that a patient has the diseasetesting of the probability that a patient has the diseaseof interest divided by the probability that the patientof interest divided by the probability that the patient

does not have the disease of interest.does not have the disease of interest. Pretest odds= pretest probability/(1Pretest odds= pretest probability/(1--pretest probability)pretest probability)


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Posttest odds of disease: as the estimate after diagnostictesting of the probability that a patient has the disease ofinterest divided by the probability that the patient does not

have the disease of interest. Posttest odds= pretest odds x LR+

Posttest probability= posttest odds/ (1+posttest odds)

a result of obtaining a positive test result, the estimated

probability of the presence of disease has risen from 0.08(pretest probability) to 0.76 (posttest probability).

Diagnostic tests that produce big changes from pretest topost-test probabilities are important and likely to be usefulto us in our practice


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Software: CAT MakerSoftware: CAT Maker


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Can you apply this valid, important evidence about

a diagnostic test in caring for your patient?

Is the diagnostic test available, affordable, accurate, and precise in your

setting? NoNoCan you generate a clinically sensible estimate of your patients pre-test

probability (from personal experience, prevalence statistics, practice

databases, or primary studies)?

yAre the study patients similar to your own?yIs it unlikely that the disease possibilities or probabilities have changed

since the evidence was gathered?

YesYes

YesYes

Will the resulting post-test probabilities affect your management and help

your patient?

y

Could it move you across a test-treatment threshold?yWould your patient be a willing partner in carrying it out?

YesYes

Would the consequences of the test help your patient?YesYes

Additional notes:


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Thank you..Thank you..

CA Diagnostic KBK1

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