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SCREENING

SCREENING. The search for unrecognized disease or defect by means of rapidly applied tests, examinations or other procedures in apparently healthy individuals. SCREENING (Conti). Testing for infection or disease in population or individuals who are not seeking health care

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SCREENING

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

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

  3. SCREENING (Conti) • The active search for disease among apparently healthy people is a fundamental aspect of prevention • To bring such examination within the reach of large masses of people with minimal expenditure of time and money • Conserve physician time • Administration of simple, inexpensive lab. Tests • Preventive care function

  4. SCREENING (Conti) • 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.

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

  6. Screening

  7. USES OF SCREENING • Case detection • Control of disease • Research purpose • Educational opportunities

  8. TYPES OF SCREENING • MASS SCREENING • HIGH RISK OR SELECTIVE SCREENING • MULTIPHASIC SCREENING

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

  10. SCREENING TEST • Acceptability • Repeatability • Validity • Yield • Simplicity • Safety • Rapidity • Ease of administration • Cost

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

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

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

  14. Evaluation of screening test

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

  16. Validity (Conti) • Specificity: • The ability of a test to identify correctly all those who do not have the disease = true negative • specificity= d / b + d X 100 • 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.

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

  18. False positive • That the patients do not have the disease are told that they have the disease in question. • 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.

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

  20. Evaluation of screening test

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

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