Screening for Disease

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  1. Screening
    “The presumptive identification of an unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not.”
  2. Multiphasic Screening
    using two or more screeening tests together among large groups of poeple
  3. Mass Screening
    screening on a large scale of total population groups regardless of risk status
  4. Selective Screening
    Screens subset sof the population at high risk for disease
  5. Case Finding (opportuistic screening)
    Use of screening tests for detection of conditions unrelated to the patient's chief complaing
  6. Mass Health Examinations
    • Population or epidemiologic surveys
    • -purpose is to gain knowledge regarding the distribution and determinants of diseases in selected populations
    • No benefit to the participant is implied
  7. Screening Progrm
    • Immediate Objective: identify people as likely or unlikely to have disease
    • Long Term Objective: reduce mortality and morbidity in a population
  8. Preimary Prevention Effort
    • Prevents disease from occurring
    • Goal is to reduce incidence
  9. Secondary Prevention Effort
    • Delays onset of and duration of clinical disease
    • Goal is to improve survival
  10. Secondary Prevention Effort
    • Delays onset of and duration of clinical disease
    • Goal is to improve survival
  11. Tertiary Prevention Effort
    • Slows disease progression; reduces sequelae
    • Goal is to improve survival
  12. HIV/AIDS Prevention Level example
    • Primary: Intervention programs that reduce risky behaviors such as needle sharing and unsafe sex
    • Secondary: Screening
    • Tertiary: use of drugs to prevent opportunistic infections (immunosuppressed)
  13. Characteristics of Appropriate diseases for screening
    • Disease is serious with severe consequences
    • Treatment is more effective at an earlier stage
    • Disease has a detectable preclinical phase (DPCP)
    • DPCP is fairly long and prevalent in the target population
  14. HIV Characteristic of Appropriate disease for screening example
    • Severe disease with very dire consequences
    • Many tretments reduce disease sequelae when giving early
    • Long and highly prevalent DPCP
  15. Validity
    • Ability of a test to distinguish between who has disease and who does not
    • Measured by sensitvity and specificty
  16. Sensitivity (Se)
    Ability of a test to identify correctly those who HAVE the disease
  17. Specifity (Sp)
    Ability of a test to identify correctly those who DO NOT have the disease
  18. Sensitivity Equation
    # individuals with disease who test positive / # individuals with disease X 100
  19. Specifity (Sp) Equation
    # individuals without disease who test negative / # indviduals without disease X 100
  20. Sensitivy and Specifity Examples
    • Sensitivity (EX= 80.0%): 80% of people with the disease test positive for the disease
    • Specifity (EX= 88.9%): 88.9% without the disease test negative for the disease
  21. Predictive Value Postive (PVP)
    Proportion of patientes T+ for the disease who actually have the disease
  22. Predictive Value Negative (PVN)
    Porportion of patients T- for the disease who DO NOT have the disease
  23. Predictive Value
    • High PVP is essential for a successful screening program
    • Program detects a large proportion of actual cases among T+
    • Low PVEP implies resources are wasted on invasive, expensive diagnostic and follow-ups
  24. Lenght Time Bias
    Screening tends to identify cases with long preclincal course, less aggressive forms of disease
  25. Summary
    • Overall goal of screening program is to improve survival
    • Se, SP, PVP, PVN are measurable characteristics of a screening test and screening program
    • PVP is dependent on prevalence and Sp
Card Set
Screening for Disease
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