Screening Programmes: Criteria & Principles for MRCP Part 1

TL;DR

Screening programmes aim to reduce disease-related morbidity and mortality by detecting disease in asymptomatic populations—but only when strict criteria are met. For MRCP Part 1, you must understand the Wilson–Jungner principles, test performance (especially PPV and prevalence), and common biases that make screening look beneficial when it is not. Most exam questions test why screening works—or fails.

Why screening programmes matter in MRCP Part 1

Screening is a high-yield topic because it blends epidemiology, ethics, and clinical reasoning. Candidates often lose marks by assuming that “earlier diagnosis is always better.” In reality, inappropriate screening can cause psychological harm, unnecessary treatment, and wasted resources—exactly the issues MRCP Part 1 likes to test.

This article supports the MRCP Part 1 hub and should be read alongside the official exam guidance and applied question practice.

👉 MRCP Part 1 overview: https://crackmedicine.com/mrcp-part-1/

What is a screening programme?

A screening programme is the systematic application of a test to apparently healthy individuals to identify those at increased risk of a disease, who may then benefit from further investigation or treatment.

Key exam distinction

• Screening → asymptomatic population

• Diagnosis → symptomatic individual

This single distinction underpins many SBA questions.

The Wilson–Jungner criteria (core principles)

Most MRCP Part 1 questions on screening are variations on these principles. You do not need the exact wording, but you must recognise when one is violated.

High-yield summary of the criteria

1. The condition is an important health problem

2. There is an effective treatment available

3. Facilities for diagnosis and treatment exist

4. There is a latent or early symptomatic stage

5. A suitable screening test exists

6. The test is acceptable to the population

7. The natural history of the disease is understood

8. There is an agreed policy on whom to treat

9. The programme is cost-effective

10. Screening is a continuous process

Exam insight: If a disease has no effective treatment, screening almost always fails—no matter how accurate the test.

Authoritative reference:UK National Screening Committee – Screening principleshttps://www.gov.uk/government/publications/uk-national-screening-committee-screening-principles

Five most tested subtopics

1. Test performance in screening

• High sensitivity is prioritised → minimise false negatives

• Specificity affects downstream harm (false positives)

• Positive predictive value (PPV) depends heavily on prevalence

Low prevalence = low PPV, even with excellent tests. This is a classic MRCP Part 1 trap.

2. Biases that exaggerate screening benefit

These biases make screening appear useful without reducing mortality.

• Lead-time bias: earlier diagnosis falsely increases survival time

• Length-time bias: slower, less aggressive disease is preferentially detected

• Overdiagnosis bias: detection of disease that would never cause symptoms

If a question mentions “improved 5-year survival” but unchanged mortality → think bias.

3. Population vs targeted screening

• Population screening → low prevalence, more false positives

• Targeted (high-risk) screening → higher PPV, fewer harms

Exam favourites

• Abdominal aortic aneurysm screening → older men

• Diabetic retinopathy screening → patients with diabetes only

4. Ethical considerations

Because screening is offered to well people, the ethical threshold is higher than for diagnostic testing.

Key issues:

• Informed consent

• Psychological harm from false positives

• Harm from unnecessary treatment (overdiagnosis)

5. When screening should not be done

Screening is inappropriate when:

• No effective treatment exists

• The test is poorly accurate or unacceptable

• Costs outweigh benefits

• Harms exceed population benefit

“Earlier detection” alone is never sufficient justification.

Screening vs case-finding (commonly tested)

Feature	Screening	Case-finding
Population	Asymptomatic	Opportunistic
Approach	Systematic invitation	Clinician-initiated
Ethics	Higher threshold	Lower threshold
Example	Cervical screening recall	BP check during GP visit

Mini-MCQ (exam-style)

A new screening test for a rare cancer has a sensitivity of 99% and specificity of 90%. The disease prevalence is 1 in 20,000. What is the most likely consequence of introducing population screening?

Answer: A large number of false positives.

Explanation: With very low prevalence, PPV remains low despite excellent sensitivity. Many healthy individuals will test positive and undergo unnecessary investigations—violating screening principles.

👉 Practise similar questions in the MRCP Qbank:https://crackmedicine.com/qbank/

Five common MRCP Part 1 traps

• Confusing increased survival with reduced mortality

• Forgetting PPV depends on prevalence

• Assuming high sensitivity alone justifies screening

• Ignoring harms of overdiagnosis

• Missing lead-time bias in statistics

Practical study checklist

Before your next mock exam, ask yourself:

• Can I explain why screening for a disease might be harmful?

• Can I identify lead-time bias in one sentence?

• Do I understand why rare diseases are poor screening targets?

• Can I distinguish screening from diagnosis instantly?

• Have I practised probability questions involving PPV?

Apply these concepts under time pressure using a full mock test:https://crackmedicine.com/mock-tests/

FAQs

What is the main aim of screening programmes?

To reduce disease-specific morbidity or mortality by detecting disease early when effective treatment exists.

Why is screening unethical in some diseases?

Because detecting untreatable or indolent disease exposes healthy people to harm without benefit.

Is high sensitivity enough to justify screening?

No. Prevalence, PPV, downstream harm, and cost-effectiveness are equally important.

Which bias is most commonly tested in MRCP Part 1?

Lead-time bias—earlier diagnosis falsely inflating survival statistics.

Sources

• UK National Screening Committee. Screening principles.https://www.gov.uk/government/publications/uk-national-screening-committee-screening-principles

• MRCP(UK). Part 1 Examination Information.https://www.mrcpuk.org/mrcpuk-examinations/part-1

• Wald NJ. Principles of Screening. Oxford Textbook of Public Health.