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8 screening.pptx
- 1. Module 3: Screening By: Nigusie Shifera(MPH/Epidmology) 8/10/2022 Screening 1
- 2. Objectives • Describe screening • Understand necessity of screening • Mention and describe the type of screening • Evaluate screening test • Describe PPV, NPV, and prevalence • Describe the public importance of Screening 8/10/2022 Screening 2
- 3. Introduction 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 Screening is not the same as diagnosis; screening tests give us information about whether the disease is likely to be present 8/10/2022 Screening 3
- 4. Introduction A screening test assesses the presence of an underlying marker that is associated with outcome of interest A diagnostic test is used to determine the presence or absence of a disease when a subject shows signs or symptoms of the disease The diagnostic test is performed after appositive screening test to establish a definitive diagnosis 8/10/2022 Screening 4
- 5. Screening… By Wondimagegn W. 5 8/10/2022
- 6. Introduction Examples Pap smear for cervical dysplasia or cervical cancer Fasting blood sugar for diabetes Blood pressure for hypertension Mammography for breast cancer pregnancy tests to screen for presence of an embryo or fetus 8/10/2022 Screening 6
- 7. Objectives of Screening • Identify unrecognized disease in apparently well persons • Reduce morbidity & Mortality • Protect society against spread of the disease • Determine the extent of the pre-symptomatic disease in the population • Provide data for research on the effectiveness of tests, programs etc… 8/10/2022 Screening 7
- 8. Criteria for selection of Screening program • We screen for disease when we have the opportunity to reduce costs and risk associated with diagnoses on large proportions of at-risk individuals • We screen for health indicators that affect population health principally, not for rare diseases • It should be under taken only, when it has potential to decrease in rate of disability /death or both • There should be accepted treatment for patients with recognized disease 8/10/2022 Screening 8
- 9. Criteria for selection of Screening program • Facilities for diagnosis and treatment should be available • There should be recognized early asymptomatic stage • There should be a suitable test method that has high validity • Screening tests should be cheaper and less invasive than best available diagnostic tool • The test should acceptable to the population 8/10/2022 Screening 9
- 10. Types of screening a) Mass screening – involves screening of a whole population b) Targeted screening – involves screening of groups with specific exposures (e.g. environmental or occupational exposures) c) Case‐finding or opportunistic screening – is restricted to patients who consult a health practitioner for some other purpose E.g. PITC d) Multiple or multiphasic screening -If more than one screening procedure is applied on the same occasion By Wondimagegn W. 10 8/10/2022
- 11. For successful screening program ideal screening test • should be inexpensive • easy to administered • minimum discomfort • the result must be valid& Reliable 8/10/2022 Screening Evaluating Test Performance
- 12. I) Validity of screening test II) Reliability (precision) 8/10/2022 Screening Evaluating screening Test Performance
- 13. Validity of a test:- is the ability to correctly categorize individual who have disease as test positive and those with out disease as test negative measures of the validity of a screening test A. Sensitivity B. Specificity C. Positive predictive value D. Negative predictive value 8/10/2022 Screening I)Validity of a Screening Test
- 14. Evaluating… • We compare the screening test against some “gold standard” • Measures of validity: sensitivity and specificity 14 8/10/2022
- 15. • Sensitivity is the ability of the test to identify correctly those who have disease(a) from all individual who have disease (a+c). 8/10/2022 Screening Sensitivity
- 16. • Specificity is the ability of the test to identify correctly those who do not have a disease(d) from all individuals free from the disease. 8/10/2022 Screening Specificity
- 29. The yield is number of cases detected by the screening program. Yield =Persons with the disease detected by the test X 100 Total screened Yield = TP X 100 TP + FN + TN + FP 8/10/2022 Screening Evaluation of screening program 29
- 30. 8/10/2022 Screening Evaluation of screening program Factors that may increase participation in screening Factors that may decrease participation in screening Knowledge of condition Disease phobia Perception of susceptibility Stigma associated with condition Perception of disease severity Unpleasant diagnostic tests and treatment Knowledge of availability of treatment Socio-economic factors (e.g. income, education, deprivation, employment) Socio-demographic factors (age, sex, ethnicity, language, creed) Accessibility of screening sites 30
- 31. Clinical setting ANC, GM, HIV/AIDS, tuberculosis , cervical ca, STIs etc Community setting Research interventions Recruitment Military , Industry Licensing Driving license Immigration Border screening etc 8/10/2022 Screening Some settings in which screening is applied 31
- 32. Quiz(10%) 8/10/2022 Screening 32 Calculate the sensitivity, Specificity, ppv, NPV, and Yield? Screening Results Characteristics of the population Disease Not disease Total Positive A 120 170 Negative 140 D C+d Total A+C 185 A+B+C+D