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

2. 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 ?

3. 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?

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

5. (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

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

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

8. 2.Why do we screen for disease?

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

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

11. 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)

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

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

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

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

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

17. (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

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

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

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

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