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Screening

Screening. Sherine Shawky, MD, Dr.PH Assistant Professor Public Health King Abdulaziz University College of Medicine shshawky@hotmail.com. Epidemiology in Medicine. Foundation of medical research Support for medical advancement Essential in medical education & practice

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Screening

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  1. Screening Sherine Shawky, MD, Dr.PH Assistant Professor Public Health King Abdulaziz University College of Medicine shshawky@hotmail.com

  2. Epidemiology in Medicine • Foundation of medical research • Support for medical advancement • Essential in medical education & practice • Boundary for biostatistics

  3. Learning Objectives • Understand the concept of screening • Understand the characteristics of health-related events suitable for screening • Recognize the characteristics of a screening program

  4. Performance Objectives • Apply screening for early detection of risk factors & diseases • Identify the factors suitable for screening • Evaluate the benefit of screening

  5. Screening Screening is the process to detect among healthy people disorders or risk factors of which they are unaware

  6. Flow diagram for a screening program Population Screening test Test -ve Test +ve Diagnostic procedures Unaffected Affected Re-screen Intervention Re-screen

  7. Types of screening • Mass • Multiple or multiphasic • Targeted • Case-finding or opportunistic

  8. Factors appropriate for screening • Important health problem • High prevalence • Natural history understood • Long latent period • Early detection improves prognosis

  9. Evaluation ofa screening program • Reliability • Feasibility • Validity • Performance • Effectiveness

  10. Reliability • Biological variation • Program method • Intraobserver variability • Interobserver variability

  11. Acceptability Quick Easy Safe Cost effectiveness Screening Diagnosis Follow-up Intervention Feasibility

  12. Validity • Sensitivity: Probability to test positive among truly affected • Specificity: Probability to test negative among truly unaffected

  13. Performance • PV+:- Probability to be affected among test positives • PV-:- Probability to be unaffected among test negatives • PCC:- Probability to be correctly classified

  14. Effectiveness • Outcome measures: • Morbidity • Disability • Mortality

  15. Effectiveness • Bias • Patient self-selection • Lead time • Length

  16. Study designs for screening 1. Correlation Studies • Use: Description of population • Strength: Suggest possibility of benefit • Limitation: Can’t test hypothesis

  17. Types: Case-control Cohorts Use: Comparison of rates Advantage: Test hypothesis Limitation: Selection Lead time length Study designs for screening 2. Analytical Studies

  18. Study designs for screening 3. Randomized Trials • Use: Comparison of rates • Strength: Most valid test of hypothesis • Limitation: Cost, ethics & feasibility

  19. Evaluation of screening *Sensitivity= TP/TA *PV+ = TP/SP *Specificity= TN/TH *PV-= TN/SN *PCC= TP+TN/GT

  20. Conclusion • Objectives of screening • Reduce disease incidence • Reduce morbidity, disability & mortality • Criteria for screening • Appropriate factor • Beneficial program

  21. Review Questions (Developed by the Supercourse team) • What is screening and what types of screening can you name? • What are the objectives of screening? • For what type of diseases would it be appropriate to set up screening programs? List characteristics. • How is screening program evaluated?

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