Screening.ppt
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Screening involves using tests to detect diseases or risk factors in asymptomatic individuals. The goal is to classify people as likely or unlikely to have a disease and ultimately reduce mortality and morbidity. Screening tests are not diagnoses, but provide information about the likelihood of a disease being present. Effective screening programs screen the entire population or high-risk groups, use valid, reliable, and acceptable tests, and improve health outcomes cost-effectively by detecting diseases earlier.
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Screening.ppt
- 1. Screening
- 2. Screening • Screening is the process to detect among healthy people disorders or risk factors of which they are unaware • Screening is the process in which we use a test to determine whether an individual likely has a particular health indicator or not or is likely to develop a particular health indicator or not
- 3. Screening • Screening is not the same as diagnosis; screening tests give us information about whether the disease is likely to be present while diagnosis is confirmation of presence of the disease e.g. Urine Pregnancy test (screening) vs Serum HCG levels (diagnostic) • A screening test assesses the presence of an underlying marker that is associated with outcome of interest e.g. Screening = Breast CA, Screening Test = Mammography 3
- 4. Flow diagram for a screening program Population Test -ve Test +ve Unaffected Affected Intervention Diagnostic procedures Screening test Re-screen Re-screen
- 6. Population screening • Immediate objective of a screening test is to classify people as being likely or unlikely of having the disease. • Ultimate objective of a screening test is to reduce mortality and morbidity.
- 7. Principles for Screening Programs 1. Condition should be an important health problem 2. There should be a recognizable early or latent stage 3. There should be an accepted treatment for persons with condition 4. The screening test is valid, reliable, with acceptable yield 5. The test should be acceptable to the population to be screened 6. The cost of screening and case finding should be economically balanced in relation to medical care as a whole 7. Long latent period (the interval between exposure to a carcinogen, toxin, or causing organism and development of a consequent disease 8. Early detection improves prognosis
- 8. Feasibility • Acceptability Quick Easy Safe • Cost effectiveness Screening Diagnosis Follow-up Intervention
- 10. Criteria for Evaluating a Screening Test Validity: provide a good indication of who does and does not have disease -Sensitivity of the test -Specificity of the test Reliability (precision): gives consistent results when given to same person under the same conditions Yield: Amount of disease detected in the population, relative to the effort. Prevalence of disease/predictive value.
- 11. Validity • To assess the validity of a screening tool in establishing the presence of disease we compare with a gold standard. • Sensitivity: True positives measures the proportion of positives that are correctly identified as such. Ideal is 100% ; 100% of cases are detected. (e.g., the percentage of sick people who are correctly identified as having the condition) • Specificity: True negatives measures the proportion of negatives that are correctly identified as such. Ideal is 100% ; 100% of non-cases are negative. (e.g., the percentage of healthy people who are correctly identified as not having the condition)
- 12. Types of Screening • Mass screening : Mass screening means, the screening of a whole population or a subgroup. It is offered to all, irrespective of the risk status of the individual. • Selective screening : High risk screening is conducted among risk populations only. • Multiphasic screening : It is the application of two or more screening tests to a large population at one time instead of carrying out separate screening tests for single diseases.
- 13. Examples of screening • Women receive regular screening tests beginning in young adulthood for cervical cancer (Pap smear) • Physicians assess blood pressure and cholesterol as screening tools for the development of cardiovascular disease • Mammography for Breast CA • Women use home pregnancy tests to screen for presence of an embryo or fetus
- 14. Example Case: Screening vs. symptom diagnosis • Person 1’s cancer detected through screening • Person 2’s cancer detected due to symptoms • Person 1 and person 2 have equal time from cancer onset to death • Time from cancer detection to death is longer in Person 1 • Lead time: The time from detection from screening and detection through symptoms afforded by screening test.