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Screening Dr Poonam R Naik Professor Department of Community Medicine Iceberg phenomena of disease Spectrum of disease Concept of screening Active search for disease among apparently healthy people Definition: Search for unrecognized disease or defect by means of rapidly applied tests, examination or other procedures in apparently healthy individuals. Screening vs diagnostic test Screening Test Diagnostic test Apparently healthy Those with indications Applied to groups Applied to single patient Single criterion Multiple criteria of evaluation Less accurate More accurate Less expensive More expensive Not a basis for treatment Basis for treatment Initiative by: Investigator Initiative by: Patients Concept of lead time Detection programmes: Time lag between disease onset and usual time of diagnosis: Long Time lag Critical points Early detection before usual time of diagnosis: Treatment should be successful Lead Time: Advantage gained by screening: Period between diagnosis by early detection and diagnosis by other means Programme benefits: Terms of its outcome Aims and objectives of screening Those who are likely to have the disease or are at increased risk of the disease under study Apparently abnormal: Medical supervision and treatment Apparently Normal: Periodic screening Terms Screening: Who are not seeking health care: Blood donors: HIV Testing Case Finding: Who are seeking health care for other reasons: HIV Testing among Tuberculosis patients Diagnostic test: To confirm or refute a diagnosis Uses of screening 1. Case detection: Prescriptive screening. People are screened for their own benefit. Initiate the treatment appropriately. Example: Pregnant women 2. Disease control: Prospective screening For the benefit of others. Early diagnosis: Effective treatment and implementation of control measures to prevent the spread 3. Research Purposes: 4. Educational opportunities: To the community Types of Screening 1. Mass screening: Should be backed up by support measures 2. High risk or selective screening: Screening for risk factors. Thereby implement control measures and thus effective. 3. Multiphasic screening: Application of two or more screening test in combination to a large group people. Expensive. Criteria for screening 1. Important public health problem (High prevalence) 2. Recognizable latent or early asymptomatic stage 3. Understanding of the natural history of the diseases 4. Availability of test to detect before the onset of signs and symptoms 5. Availability of confirmatory tests 6. Effective treatment 7. Agreement on cut off criteria for treatment consideration 8. Expected benefits (Life saving should exceed the cost and risks involved) Think Time 1. Paraphrase screening 2. Enumerate 4 differences between screening test and diagnostic test 3. Lead time concept: Discuss in view of diseases with small and long time gap 4. Correct the error: HIV testing in all antenatal women is an example of screening 5. Enumerate the types of screening 6. 3 uses of screening