Preventive Medicine
Core concepts
Screening principles, immunisation, lifestyle counselling, and risk stratification dominate. Know the criteria for a valid screening test and the difference between primary, secondary, and tertiary prevention.
Question traps
- Screening criteria. A valid screening programme requires a common condition, an acceptable test with high sensitivity and specificity, an effective treatment, and evidence that early detection improves outcomes. Lead-time bias and length-time bias are classic distractors.
- Sensitivity vs specificity. Sensitivity = true positives / all diseased. Specificity = true negatives / all healthy. A highly sensitive test is good for ruling out (SnNout); a highly specific test is good for ruling in (SpPin).
- Primary vs secondary prevention. Vaccination and smoking cessation are primary; screening is secondary; rehabilitation is tertiary.
- Immunisation schedules. Know live vs inactivated vaccines and contraindications (e.g. live vaccines in immunocompromised patients and pregnancy).
- Overdiagnosis. Screening detects indolent disease that would never cause harm; this is a frequent conceptual question.
Worked rule of thumb
Use SnNout / SpPin: a highly Sensitive test, when Negative, rules out; a highly Specific test, when Positive, rules in. This resolves most test-performance questions quickly.
Counselling
Brief interventions (e.g. 5As: Ask, Advise, Assess, Assist, Arrange) are the standard for smoking cessation.