This document provides guidance on critically appraising articles about diagnostic tests using the four steps of evidence-based medicine: ask, acquire, appraise, and apply. It discusses assessing whether diagnostic test results are valid by evaluating the study design, spectrum of patients, and blinding of test interpretation. Key results include likelihood ratios which indicate how much a test result changes the probability of disease. Application involves considering test reproducibility, applicability to practice, and whether test results will change management and improve patient outcomes with acceptable risks and available treatment.

1. CRITICAL APPRAISAL OF ARTICLES
ABOUT DIAGNOSTIC TEST
Dr. Faisal Al Haddad
Consultant of Family Medicine & Occupational Health
Incharge of Occupational Health Unit
PSMMC

2. Process of EBM
 Ask
 Acquire
 Appraise
 Apply

3. (Critical Appraisal (Diagnosis
 Are
the results valid?
 What
 Will
are the results?
the results help me in caring for my patients?

4. ?I Are the results valid

5. Was there an independent, blind. 1
?comparison with a reference standard
 Is
reference standard used acceptable?
 Were
the investigators interpreting a test
blinded to the results of the other test?

6. Did the patient sample include an appropriate. 2
spectrum of patients to whom the diagnostic
?test will be applied in clinical practice
 Representative
of the patients in whom the test is to
be used.
 Varying
 Varying
 Varying
presentations of the target disorder
severity of the target disorder
stage of the target disorder

7. 3. Did the results of the test being evaluated
influence the decision to perform the
reference standard?
 Was
the gold standard applied to subjects in
whom the study investigation was negative?
 Were
both reference standard and test under
investigation applied to all patients?

8. Were the methods for performing .4
the test described in sufficient detail
?to permit replication
 Preparation
of patient?
 Performance
 Analysis
of test?
and interpretation of results?

9. ?II What are the Results

10. What is Likelihood Ratio
NLR: Ratio of the probability of a false negative result if the disease is present
to a true negative result if the disease is absent. FN/TN
The extent to which a negative test decreases the likelihood that a patient has disease
The less the NLR, the less the likelihood that a patient with negative test has disease
e.g. CT scan with NLR of 0.05
-ve CT scan indicates that the pat is free from PE
PLR: Ratio of the probability of a true positive result if the disease is present to
a false positive result if the disease is absent. TP/FP
The extent to which a positive test increases the likelihood that a patient has disease.
The more the PLR, the more the likelihood that a patient with positive test has disease
e.g. CT scan with PLR of 20
+ve CT scan indicates that the pat has PE

12. III Will the results help me in
?caring for my patients

13. 1. Will the reproducibility of the test result
and its interpretation be satisfactory in my
clinical setting?

14. Are the results applicable to the. 2
?patient in my practice
 Similar
distribution of disease severity?
 Similar
distribution of competing diseases?
 Does
the patient meet the study inclusion criteria?
 Does
the patient violate any of exclusion criteria?

15. Will the results change my management. 3
?strategy
Are the test LRs high or low enough to shift post-test
probability across a test or treatment threshold?

16. Pulmonary embolism management:

Treatment threshold 80%

Test threshold 10%
VQ scan properties:

PLR 20

NLR 0.36
78-year-old woman chest pain and shortness of breath 10
days after surgery

Pretest probability of pulmonary embolism 70%.

Posttest probability with abnormal VQ scan result 97%

Posttest probability with normal VQ scan result 19%
28-year-old man chest pain and shortness of breath
experiencing a high level of anxiety.

Pretest probability of pulmonary embolism 20%

Posttest probability with abnormal scan result is 85%

Posttest probability with normal VQ scan result is 2%

18. Will patients be better off as a. 4
?result of the test
 Is
target disorder dangerous if left undiagnosed?
 Is
test risk acceptable?
 Does
effective treatment exist?

19. THANK YOU

20. ANY
?QUESTIONS