Screening for Disease: Part One By:Dr.Yossra K.Al-Robaiaay Assistant professor FICMS (FM)

What does “screening” mean? Diagnostic and screening tests have major differences...why? What is the goal of screening test? What are the purposes of screening ?

What do we screen for? What makes a disease or risk factor an appropriate target for screening? What are the characteristics of a good screening test?

What is a gold standard? What is the meaning of validity ,sensitivity & specificity ? Predictive values?

(a+b) Total Test positive   Screening test Gold standard Test Disease Disease Free Total Positive Negative (a) True Positive (b) False Positive (a+b) Total Test positive (c) False Negative (d) True Negative (c+d) Total Test Negative (a+c)Total Disease positive (b+d) Total Disease Negative (a+b+c+d) Grand Total

Accuracy of the test? Reliability of the test? Relation between prevalence & predictive values?

1.Differentiate between doing test for a patient, and screening?

2.Why do we screen for disease?

3. How can we screen for low-prevalence diseases?

4. Some tests may give variable results on re-testing, why?

5. The screening test should be both reliable & valid. Why? Answer: Unreliable tests are confusing even if valid. Invalid tests are meaning less even if reliable (explain)

6. Which do you prefer, a sensitive, or a specific test?  

7. What are the drawbacks of using a test with low sensitivity?

8. What are the consequences of using a test with low specificity?

9. Do you agree that specificity is the ability of a screening test to be positive only if the disease is present?

10. How can we find out the prevalence of a disease in a community using a screening test survey? Answer:

(a+b) Total Test positive   Screening test Gold standard Test Disease Disease Free Total Positive Negative (a) True Positive (b) False Positive (a+b) Total Test positive (c) False Negative (d) True Negative (c+d) Total Test Negative (a+c)Total Disease positive (b+d) Total Disease Negative (a+b+c+d) Grand Total

11. If the screening criterion to detect glaucoma is set at 22mm Hg, what happens to the sensitivity & specificity of the test?  

12. If the screening criterion to detect glaucoma is set at 26mm Hg, how do the sensitivity & specificity change?  

13. What is the relation between sensitivity & specificity 13. What is the relation between sensitivity & specificity? Answer: It is Reciprocal relation. (Explain).

14. Where do you put the criterion if this screening test is to be used?