Disease Prevention and Screening
Evidence-based screening
Know the major recommended screens and their intervals: cervical cancer (cytology/HPV), breast cancer (mammography), colorectal cancer (FIT/colonoscopy), hypertension, diabetes (risk-based), lipids, and vaccination schedules. In the Arab region, consider hepatitis B/C, consanguinity-related genetic disease, and vitamin D deficiency. Screening recommendations differ by organisation (USPSTF, WHO, national programmes) - answer according to the stem's stated context.
Immunisation
Understand live vs inactivated vaccines, contraindications (pregnancy, severe immunodeficiency for live vaccines), cold chain, and catch-up schedules. Herd immunity thresholds vary (e.g., measles ~95%).
Risk communication and counselling
Absolute vs relative risk is a classic trap. A 50% relative reduction from 2% to 1% is a 1% absolute reduction; NNT = 100. Number needed to treat/screen and number needed to harm should guide shared decisions.
Traps
- Recommending a test outside its evidence-based age/interval.
- Confusing screening (asymptomatic) with case-finding/diagnosis (symptomatic).
- Overlooking vaccination contraindications in pregnancy or immunosuppression.
- Misinterpreting relative risk as absolute benefit.
Worked example
A 55-year-old asymptomatic woman: recommend colorectal screening (FIT annually or colonoscopy per programme) and mammography per local guideline. Do not order a diagnostic colonoscopy for screening without indication; do not screen a 30-year-old average-risk woman with mammography.
Rule of thumb
Screen when the condition is important, detectable early, treatable, and the benefit outweighs harm - and always quote absolute numbers.