SCREENING FOR DISEASE Iceberg Phenomenon of Disease TIP– What physician sees in community SUBMERGED PORTION: Hidden Mass of disease (Latent, Inapparent, presymptomatic, undiagnosed & Carriers) Examples: Diabetes, hypertension, anemia, malnutrition, mental illnesses etc Iceberg phenomenon Detection and control of this Hidden Mass of disease is a challenge to preventive medicine. Especially NCDs. Earlier ANNUAL / PERIODIC HEALTH CHECK UPs were used, For early detection of hidden diseases. DISADVANTAGES of Health check ups. 1. 2. 3. EXPENSIVE NEED MORE PHYSICIAN’s TIME NOT APPLICABLE for MASS Thus concept of SCREENING emerged Active search for disease Apparently healthy people among DEFINITION OF SCREENING Search for unrecognized disease or health problem by means of rapidly applied tests, examinations or other procedures in APPARENTLY HEALTHY INDIVIDUALS Screening differs from periodic health examinations by 1) 2) 3) Wide application (Masses) Relatively inexpensive Needs very little physicians time AIMS OF SCREENING 1) 2) 3) To sort out those at increased risk of disease from apparently healthy To bring those apparently abnormal under medical supervision & treatment Early diagnosis & treatment to favorably change the natural history of disease Screening Vs. diagnostic test Initiative from provider Apparently healthy Applied to groups Results: arbitrary & final Basis: one criterion or cut-off. Less accurate Less expensive Not a basis for treatment Initiative from patient SICK Single patient Not final Signs + symptoms + lab tests More accurate More expensive Basis for treatment Concept of LEAD TIME Screening is applied for those diseases which have sufficiently long “ TIME LAG ” between disease onset and usual time of diagnosis TIME LAG Two Critical points 1) First possible point 2) Final critical diagnosis These critical points determine 1) Severity of disease 2) success of any treatment in reversing disease process LEAD TIME is time - advantage gained by screening i.e. between diagnosis by early detection & usual time of diagnosis[ if no screening was done.] Uses of Screening - 4 1) Case detection (Prescriptive screening) Presumptive identification of unrecognized disease which is not arising from peoples’ request. Done for their own benefit. 2) Control of diseases (Prospective screening) People screened for the benefit of others Screening immigrants for HIV, TB , Bird flu etc Streptococcal infections --- to prevent RHD. 3) Research purposes: Uses of Screening To study natural history of diseases Eg: Chronic non-communicable diseases. 4) Educational purposes: Creating public awareness about diseases & educate health professionals Eg: Diabetes, Hypertension. TYPES of SCREENING - 3 1) MASS SCREENING: Whole population/sub-group irrespective of individual’s risk for disease Disadvantage : Not cost-effective 2) SELECTIVE / HIGH RISK SCREENING: Those people defined as high risk by epidemiological studies. TYPES of SCREENING Parous women for Cervical Cancer. Family members of Diabetics, Hypertensives, Breast cancer patients. Screening for RISK FACTORS for CHD Ex: Cholesterol, BP. Advantage: COST-EFFECTIVE 3) MULTIPHASIC SCREENING Application of two or more screening tests in combination to large number of people at the same time Example: Health questionnaire Clinical examination Lab investigations – BS , RFT. Audiometry Visual acuity tests. Issues related to screening. Prior decision should be made regarding the cut off point taking into consideration – disease prevalence, lethality of the disease - higher sensitivity of the test. Apply selectively to those people most likely to benefit from it – selection based on age, sex, occupation, medical & family history. Should be integrated into the existing health services and not developed in isolation. Ensure regular patient follow –up. CRITERIA for SCREENING Any screening program has to be justified ETHICALLY SCIENTIFICALLY & FINANCIALLY. Both DISEASE and TEST should fulfill some criteria. CRITERIA for the DISEASE 1) Important public health problem 2) Recognizable latent period (early asymptomatic stage) 3) Natural history of the disease should be adequately understood 4) TEST available to detect disease prior to onset of signs & symptoms 5) Facilities exist for confirmation of diagnosis CRITERIA for the DISEASE 6)Effective treatment available. 7) Agreed on policy about whom to treat as patients 8) Evidence that early diagnosis & treatment decreases morbidity/mortality 9) Expected benefits of early detection outweigh risks and costs. CRITERIA for the TEST 1. 2. 3. 4. 5. 6. 7. 8. ACCEPTABILITY REPEATABILITY (RELIABILITY) VALIDITY YIELD SAFETY COST SIMPLICITY EASE of ADMINISTRATION.
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