Screening and Health Promotion
Screening is testing apparently healthy people to detect disease earlier, and health promotion is enabling people to increase control over their health. The Board tests the criteria a screening programme must satisfy, the biases that mislead, and the behaviour-change models used in the consultation.
Core rules
- Wilson and Jungner criteria: the condition must be important and have a recognisable latent stage; there must be an acceptable, valid test; treatment must be effective and evidence-based; the programme must be cost-effective and equitable; and there must be agreed policy on whom to treat.
- Screening biases: lead-time bias (earlier diagnosis looks like longer survival without changing the date of death), length bias (slow, mild disease is over-represented), overdiagnosis (detecting disease that would never have harmed), and selection bias in volunteers.
- Established programmes: mammography for breast cancer in the 50-69 age group, usually every two years; cervical cytology or HPV testing from about 25 to 65; colorectal screening from around 50 using faecal immunochemical testing or colonoscopy; blood pressure measurement in all adults; lipid and glucose screening in those at risk; a single abdominal aortic aneurysm ultrasound in men aged 65 to 75; osteoporosis assessment with DEXA in high-risk postmenopausal women.
- Behaviour change: Prochaska's stages are precontemplation, contemplation, preparation, action and maintenance (with relapse). Motivational interviewing uses open questions, affirmation, reflection and summarising to build change talk. The 5As are Ask, Advise, Assess, Assist, Arrange.
- Health promotion models include the health belief model (perceived susceptibility, severity, benefits, barriers, cues to action) and the Ottawa Charter (healthy public policy, supportive environments, community action, personal skills, reorientation of services).
Worked example
A 58-year-old smoker attends for a cough. Reasoning: use the 5As. Ask about smoking and record pack-years, advise quitting clearly, assess readiness using the stages of change, assist with nicotine replacement and a quit date, and arrange a follow-up call in one week. He is in contemplation, so give a brief motivational intervention rather than a lecture. Also check blood pressure and arrange colorectal screening, but avoid ordering a chest X-ray as a screen unless symptoms indicate it.
Traps that cost marks
- Confusing screening with diagnostic testing in symptomatic patients.
- Quoting improved survival as proof of screening benefit when lead-time bias is present.
- Assuming a normal test excludes disease; no screening test is perfect.