2. SCREENING TTTThe search for unrecognized disease or defect by means of rapidly applied tests, examinations or other procedures in apparently healthy individuals

3. SCREENING (Conti) TTTTesting for infection or disease in population or individuals who are not seeking health care AAAActive search for disease among apparently healthy people

4. TTTThe active search for disease among apparently healthy people is a fundamental aspect of prevention TTTTo bring such examination within the reach of large masses of people with minimal expenditure of time and money CCCConserve physician time AAAAdministration of simple, inexpensive lab. Tests PPPPreventive care function

5. SSSScreening test is not intended to be a diagnostic test. It is only an initial examination. Those who are found to have positive test results are referred to a physician for further diagnosis and treatment.

6. AIMS AND OBJECTIVES TTTTo sort out from a large group of apparently healthy persons who likely to have the disease TTTTo sort out from a large group of apparently healthy persons who are at increased risk of disease under study TTTTo bring those who are apparently abnormal under medical supervision and treatment. EEEEarlier diagnosis and subsequent favourably alters the natural history of the disease in a significant proportion of those who are identified as positive.

7. Screening Screening test Diagnostic test Done on apparently healthy Done on those who are sick Applied to groups Applied to single patient Results are final Diagnosis is not final Based on one criteria Based on evaluation of S/S Less accurate, expensive More accurate, expensive Not basis for treatment Basis for treatment Initiative comes from investigator Initiative comes from a pt.

8. USES OF SCREENING CCCCase detection CCCControl of disease RRRResearch purpose EEEEducational opportunities

9. TYPES OF SCREENING MMMMASS SCREENING HHHHIGH RISK OR SELECTIVE SCREENING MMMMULTIPHASIC SCREENING

10. Criteria for screening DDDDISEASE: IIIImportant Health problem-high prevalence rate RRRRecognizable latent period TTTTest that detects disease prior to the onset of signs and symptoms FFFFacilities must be available to confirm the diagnosis TTTThere is an effective treatment GGGGood evidence that early detection and treatment reduces morbidity and mortality EEEExpected benefits must exceed risk and cost.

11. SCREENING TEST AAAAcceptability RRRRepeatability VVVValidity YYYYield SSSSimplicity SSSSafety RRRRapidity EEEEase of administration CCCCost

12. Repeatability RRRReliability, precision, reproducibility TTTTest must give consistent result when repeated more than once on the same individual or material under the same conditions. RRRRepeatability depends upon three major factors:

13. Repeatability (Conti) AAAA). Observer variation IIIIntra observer variation IIIInter observer variation BBBB). Biological (subject) variation CCCC). Errors relating to technical methods

14. VALIDITY WWWWhat extent the test accurately measures which it purports to measure. IIIIt expresses the ability of a test to separate or distinguish those who have a disease from those who do not. VVVValidity has two components: SSSSensitivity SSSSpecificity

15. Evaluation of screening test SCREENING TEST RESULT DIAGNOSIS TOTAL DISEASED NOT DISEASED Positive true positive (a) false positive (b) A + b Negative false negative (c) true negative (d) C + d Totala+c b + d A+ b+ c+ d

16. Validity (Conti) SSSSensitivity TTTThe ability of a test to identify correctly all those who have the disease = true positive SSSSensitivity= a / a + c X 100 99990% sensitivity means that 90% of diseased people screened by test will give true positive result and remaining 10% false negative result.

17. SSSSpecificity: TTTThe ability of a test to identify correctly all those who do not have the disease = true negative sssspecificity= d / b + d X 100 99990% specificity means that 90% of non diseased people screened by test will give true negative result and remaining 10% of non diseased people screened by the test will be wrongly classified as diseased when they are not.

18. False negative IIIIt means that patients who actually have the disease are told that they do not have the disease. AAAA screening test which is very sensitive has few false negatives. TTTThe lower the sensitivity, the larger will be the number of false negatives.

19. False positive TTTThat the patients do not have the disease are told that they have the disease in question. NNNNormal healthy people will be subjected to further diagnostic tests and will cause anxiety, inconvenience, discomfort and expense----until freedom from the disease is established.

20. Validity PPPPredictive value of a test: IIIIt reflects the diagnostic power of the test. IIIIt measures the performance of a screening test PPPPredictive value of a positive test indicates that probability that a patient with a positive test result has, in fact, the disease in question. MMMMore prevalent disease----more predictive value of a positive screening test

21. Evaluation of screening test SCREENING TEST RESULT DIAGNOSIS TOTAL DISEASED NOT DISEASED Positive true positive (a)=40 false positive (b)=20 A + b=60 Negative false negative (c)=100 true negative (d)=9840 C + d=9940 Totala+c=140 b + d=9860 A+ b+ c+ d =10000

22. Validity SSSSensitivity =40/140X100=28.57% TTTTrue positive SSSSpecificity = 9840/9860X100=99.79% TTTTrue negative FFFFalse negative=100/140X100=71.4% FFFFalse positive=20/9860X100=0.20% PPPPredictive value of a positive test= a / ( a + b) =40/60X100=66.65% PPPPredictive value of a negative test = 9840/9940X100=98.9%