Preventive Medicine
Preventive medicine questions cover primary, secondary, and tertiary prevention, plus screening principles. Candidates must understand the criteria for a valid screening program: important disease, accepted treatment, detectable early stage, acceptable test, and agreed policy on whom to treat. Know vaccination principles, contraindications, and the difference between live and inactivated vaccines. Understand risk-factor modification, counseling, and the interpretation of screening test performance (sensitivity, specificity, predictive values, and why prevalence changes predictive value).
Traps: confusing sensitivity with positive predictive value; recommending screening outside the indicated age or risk group; giving a live vaccine to an immunocompromised patient; assuming a negative test rules out disease when prevalence is high.
Worked example: a test with high sensitivity and specificity is used in a low-prevalence population. Most positive results will be false positives. This is why confirmatory testing follows a positive screening result, and why screening programs target higher-risk groups.
Rule of thumb: a positive screening test is a hypothesis, not a diagnosis. Confirm before treating.
Key concepts: levels of prevention, screening criteria, vaccine types and contraindications, and test-performance interpretation.