Practice

Diagnosis in General Practice

Diagnosis using “test of treatment”

BMJ 2009; 338 doi: 10.1136/bmj.b1312 (Published 24 April 2009)
Cite this as: BMJ 2009;338:b1312

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  1. Paul Glasziou, professor of evidence based medicine ,
  2. Peter Rose, university lecturer ,
  3. Carl Heneghan, senior clinical research fellow ,
  4. John Balla, visiting fellow
  1. 1Centre for Evidence Based Medicine, Department of Primary Health Care, University of Oxford, Oxford OX3 7LF
  1. Correspondence to: P Glasziou paul.glasziou{at}dphpc.ox.ac.uk

    Tests of treatment are commonly used when the diagnosis is uncertain, but can have pitfalls. The accompanying article (doi:10.1136/bmj.b1218) gives an example of how test of treatment can be used

    What is test of treatment?

    Though ideally we should have a clear diagnosis before starting treatment, such certainty is not always possible. Sometimes this uncertainty can be resolved by using the treatment as the test that confirms the diagnosis.1 For example, if we are unsure if a patient’s airway obstruction has a reversible element, a trial of steroids can test this: a sufficient response is then considered evidence of reversibility. At other times the test of treatment is not planned, but the failure to respond to treatment as expected leads to a rethink of the diagnosis. In this brief review we discuss different uses of the “test of treatment,” its reliability as a diagnostic tool, and how its use might be improved (for a specific example of its use, see the accompanying article on chronic cough2).

    When is it used?

    As illustrated in figure 1⇓, a “test of treatment” is one strategy for the final stage of arriving at a diagnosis. It is appropriate when a single diagnosis is highly probable but not certain, when an available treatment works for most patients if the diagnosis is correct, and when there is a measurable short term outcome or surrogate. Such tests are …

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