Endgames Statistical question

Screening

BMJ 2009; 338 doi: https://doi.org/10.1136/bmj.b1038 (Published 19 March 2009) Cite this as: BMJ 2009;338:b1038
  1. John Fletcher, clinical epidemiologist
  1. 1BMJ, London WC1H 9JR
  1. jfletcher{at}bmj.com

    When thinking about performing a screening test on an asymptomatic patient to detect a disease, which of the following criteria should ideally be fulfilled?

    • a) The test specificity should be high

    • b) The disease should be rare

    • c) An effective treatment should be available

    • d) Everyone should receive the screening test and the “gold standard” diagnosis

    • e) The natural course of the disease should be well described

    Answer

    c, e—A specific test is one that is seldom wrong when positive and may be used to confirm a diagnosis. However, in screening the important first step is not to miss anyone who may have the condition being screened for. This requires a test with high sensitivity.

    Screening for rare diseases is usually a compromise. The disadvantage is that most people put through testing will not benefit and may be exposed to inconvenience or even harm depending on the nature of the testing. A rare disease would need a particularly cheap accurate test, and the disease would need to be quite serious and amenable to treatment. Some neonatal screening programmes fall into this category—for example, screening for hypothyroidism.

    Answer d) applies to a research study that is evaluating a screening test but is not appropriate to routine practice.

    Answers c) and e) follow from Wilson and Junger’s criteria for screening. These are of historical interest and are often referred to. Others have added to them over time.

    • 1. The condition being screened for should be an important health problem

    • 2. The natural history of the condition should be well understood

    • 3. There should be a detectable early stage

    • 4. Treatment at an early stage should be of more benefit than at a later stage

    • 5. A suitable test should be devised for the early stage

    • 6. The test should be acceptable

    • 7. Intervals for repeating the test should be determined

    • 8. Adequate health service provision should be made for the extra clinical workload resulting from screening

    • 9. There should be fewer risks, both physical and psychological, than benefits

    • 10. The costs should be balanced against the benefits

    Notes

    Cite this as: BMJ 2009;338:b1038

    View Abstract

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