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Screening for diseases.pptx
- 3. CLINICAL DISEASE HIDDEN BURDEN OF DISEASE o Sub clinical cases o Carriers o Undiagnosed cases o Presymptomatic ICEBERG PHENOMENON Introduction
- 4. Screening is considered secondary prevention
- 5. Definition For Screening The presumptive identification of those who probably have disease from those who do not have By means of rapidly applied tests in apparently healthy individuals.
- 6. Risk factors pathogenesis Onset 1 st possible point of diagnosis Critical point of diagnosis Signs and symptoms Usual point of diagnosis
- 7. Risk factors pathogenesis Onset 1 st possible point of diagnosis Critical point of diagnosis Signs and symptoms Usual point of diagnosis Latent period
- 8. Risk factors pathogenesis 1 st possible point of diagnosis Critical point of diagnosis Signs and symptoms Usual point of diagnosis Lead time
- 9. Risk factors pathogenesis 1 st possible point of diagnosis Critical point of diagnosis Signs and symptoms Usual point of diagnosis Screening time
- 10. TYPES OF SCREENING Mass screening • Whole population • Screening of • Ca breast • Ca cervix • HIV High risk screening • Group of population • Screening of • Defence people • Age groups • High risk groups Multipurpose screening • To do More than one test done simultaneously to detect more than one disease • Screening of pregnant women for VDRL, HIV, HBV Multiphasic screening • Various diagnostic procedures are employed during the same screening program • DM - FBS, Glucose tolerance test
- 11. TYPES OF SCREENING People screened for their own benefit Case detection Secondary level prevention Examples • Breast lump – mammography for CA breast • Vaginal or post coital bleed – Pap smear for cervical CA • DM – Fasting and Post –prandial blood sugar Prescriptive screening People screened for others benefit Disease control Primary level prevention Examples • HIV testing in all ANC females to prevent transmission • Immigrants for infectious diseases Prospective screening
- 12. USES OF SCREENING 02 Control of disease • Prospective screening • Others benefit • Screening of immigrants for Ebola, Tb • Screening for HIV,STD’s 03 Research purposes • To know the Natural History of diseases like cancer and ,HTN. • Initial screening –Prevalence estimate • Subsequent screening – an Incidence figure 01 04 Case Detection o Prescriptive screening o Own benefit o Neonatal screening Educational opportunities • Acquisition of information of public health relevance • Creating public awareness • For educating health professionals
- 13. Screening tests Diagnostic tests Done on apparently healthy people Done on sick or ill people Applied to groups Applied to single patient Results are final Diagnosis is not final Based on one criteria and cut off Based of evaluation of signs and symptoms and lab findings Less accurate More accurate Less expensive More expensive Not a basis for treatment Used as a basis for treatment Initiative comes from investigator Initiative comes from patient
- 14. Effective treatnment A test that can detect the disease before signs and symptoms Natural history to be known Latent or early asymplomatic stage Important health problem DISEASE CRITERIA FOR SCREENING
- 15. Expected benefits of early detection should exceed the risks and costs Good evidence Early detection ant treatment reduces morbidity and mortality Policy concerning who to treat as patients Facilities for conforming diagnosis DISEASE CRITERIA FOR SCREENING
- 16. Simplicity, Safety, Rapidity, easy and cost effective Yield Validity (accuracy) Repeatability/ Reliability/Precision Acceptability SCREENING TEST CRITERIA FOR SCREENING
- 17. Simplicity, Safety, Rapidity, easy and cost effective Yield Validity (accuracy) Repeatability/ Reliability/Precision Acceptability SCREENING TEST The test should not be: • Painful. • Unsafe. • Discomforting / Embarrassing. • Acceptable to those undergoing it
- 18. Simplicity, Safety, Rapidity, easy and cost effective Validity (accuracy) Repeatability/ Reliability/Precision Acceptability Yield SCREENING TEST The amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of the screening program
- 19. Simplicity, Safety, Rapidity, easy and cost effective Yield Validity (accuracy) Repeatability/ Reliability/Precision Acceptability SCREENING TEST • VALIDITYISTHEACCURACY OFATEST • ACCURACY: "how close is result ofa test to itstruevalue?" • REPEATABILITY : The results should be consistent when repeated more than once on same individual • RELIABILITY ISTHE PRECISION OF A TEST • PRECISION: "how close arethe results of a test on repetition?"
- 20. Simplicity, Safety, Rapidity, easy and cost effective Yield Validity (accuracy) Repeatability/ Reliability/Precision Acceptability SCREENING TEST • REPEATABILITY : The results should be consistent when repeated more than once on same individual • This is not possible because of the variations that cause the test not to yield the same result • 3 types of observer variations ● Variation in the results of the test conducted over a short period on the same individual ● EX : BP measured over short interval INTRASUBJECT ● Variation in the test due to the same observer examining the result at different times ● EX: Two readings of BP by same observer INTRA-OBSERVER ● Variation in the results of the test due to multiple observers examining the result ● EX: Chest X- ray by two different Radiologists INTER-OBSERVER
- 21. Simplicity, Safety, Rapidity, easy and cost effective Yield Repeatability/ Reliability/Pre cision Acceptability SCREENING TEST Validity (accuracy) Predictive value
- 22. Predictive value
- 23. D+ Disease present D- Disease absent T+ Tested positive TP true positive FP False positive T- Tested negative FN False negative TN True negative Probability of having tested +ve out of total diseased population Sensitivity (Sn) = TP/TP + FN = TP/D+ FN error rate = FN / FN + TP = FN / D+ = 1 – Sn Probability of having tested -ve out of total diseased population
- 24. D+ Disease present D- Disease absent T+ Tested positive TP true positive FP False positive T- Tested negative FN False negative TN True negative Probability of having tested -ve out of total healthy population Specificity (Sp) = TN/TN + FP = TP/D- FP error rate = FP / FP + TN = FP / D- = 1 - Sp Probability of having tested +ve out of total healthy population
- 25. D+ Disease present D- Disease absent T+ Tested positive TP true positive FP False positive T- Tested negative FN False negative TN True negative Predictive value Probability of having the disease out of total tested +ve population. Probability of having no disease out of total tested -ve population. PPV (positive predictive value) = TP / TP + FP = TP / T+ NPV (negative predictive value) = TN / TN + FN = TN / T-
- 26. CUT – OFF POINT
- 27. CUT – OFF POINT
- 28. CUT – OFF POINT
- 29. DISADVANTAGES OF SCREENING • FALSE NEGATIVES : If a person with disease is labelled Negative • False reassurance • Ignores signs and symptoms • Postponement of treatment • Detrimental to overall health • FALSE POSITIVES : If a person without disease is labelled Positive • Further testing with long and expensive tests • Discomfort ,inconvenience , anxiety • Burden of health facilities • Emotional trauma
- 30. EVALUATION OF SCREENING PROGRAMS • Experimental • Randomised control trail • Non experimental • Cohort study • Case – control study • Ecological study
- 31. SCREENING TESTS • Pregnancy • Anaemia • Rh status • Cardiovascular diseases • HIV • Infancy • Congenital heart disease • Spina bifida • Hearing defects • Visual defects • Middle age • Cancer • HTN • DM • Elderly • Nutritional disorders • Cancer • TB • Cataract
- 32. QUESTION TIME!!
- 33. Out of 100 people having lung cancer 60 tested positive by a new screening test . Out of 900 people who don’t have lung cancer 300 tested positive . What will be the numerator while calculating sensitivity and its value? A. True positive , 60 B. False positive , 300 C. True negative , 600 D. False negative , 40 D+ Disease present D- Disease absent Total T+ Tested positive 60 TP 300 FP 360 T- Tested negative 40 FN 600 TN 640 Total 100 900 1000 Sensitivity (Sn) = TP/TP + FN 60/60+40 = 60%
- 34. In the following flow chart , point A to C is called? A. Screening time B. Lead time C. Lag time D. Generation time
- 35. Which of the following is an example of prospective screening? A. Cervical pap smear in a 40 year old patient B. Neonatal screening of a new born baby for hypothyroidism C. Screening of immigrants to a country D. Urine for sugar screening in a 40 year old man
Editor's Notes
- Prescriptive based on symptomatology
- Prevalence all cases at a point of time Incidence no of new cases
- To distinguish btw false positive and false negative
- IN case of lethal diseases cut of points can be set low bescuse of more sensitivity
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