A health board is evaluating a proposal to screen a defined population for a cancer using a new blood test. A surgical trainee on the committee is asked which principles determine whether a screening programme is justified. Which set of criteria is correct?
- AAny test that reliably detects the disease earlier than symptoms would, automatically justifies the introduction of a national population screening programme for that disease
- BScreening is justified whenever a disease is fatal, regardless of test performance
- CThe only criterion is cheapness of the test
- DWilson and Jungner: an important condition with a detectable early stage, an accurate acceptable test, effective early treatment, and benefits outweighing harms and costs
- EScreening programmes need no evaluation once started
Show answer and explanation
Correct answer: D
The Wilson and Jungner criteria (WHO, 1968) remain the framework by which every screening programme — breast, bowel, cervical, and AAA in UK practice — is judged. The disease must matter (burden), have a recognisable latent or early symptomatic stage, and a natural history understood well enough to know that intervening early changes outcomes. The test must be valid (sensitive and specific), safe, acceptable to the population (uptake determines effectiveness), with an agreed policy on whom to treat. The system must be able to deliver: confirmed diagnosis and effective treatment for screen positives, continuously, at justifiable cost. The modern additions are the biases and harms that make screening deceptively attractive: lead-time bias (earlier diagnosis lengthens apparent survival without postponing death), length-time bias (screening preferentially finds indolent disease), and overdiagnosis (detecting disease that would never have harmed — the central controversy in prostate and part of the breast debate) — which is why programmes are validated by randomised evidence of disease-specific mortality reduction, not by survival statistics.
Why the others are wrong: A and B — early detection without effective early treatment, or with an inaccurate test, produces anxiety, harm and cost without benefit. C — cost matters only within effectiveness. E — programmes require continuous quality assurance and re-evaluation.
Key point: Screening is justified only when the Wilson-Jungner chain holds — important disease, detectable early stage, valid acceptable test, effective early treatment, deliverable programme, harms and biases (lead-time, length-time, overdiagnosis) outweighed — proven by mortality reduction in trials, never by survival figures alone.
Guidelines: Wilson and Jungner principles (WHO 1968), applied in the UK by the National Screening Committee: an important condition with a detectable latent phase, an acceptable and valid test, effective earlier treatment, and programme benefit outweighing harm at reasonable cost.