Are Medical Tests Accurate?

February 16, 2006

Anyone who visits a doctor is familiar with diagnostic tests. The

results are either negative (no disease), or they indicate an

underlying disease and are used to guide treatment decisions. But how

reliable is the evidence from studies evaluating the accuracy of

medical tests?

To determine a test's accuracy, researchers compare its results with

those of a " gold standard " -- usually a more definitive test but one

that is too costly, time-consuming or risky. However, shortcomings in

study design and methodology are known to affect estimations of

accuracy.

In this issue, Anne Rutjes and colleagues report on their analysis of

487 primary studies of test evaluations to determine if the published

results were accurate. Surprisingly, they found that only one of the

studies had no design deficiencies. Studies that included patients

with severe disease and healthy control subjects were most likely to

overestimate accuracy. Thus, the test would perform well among

patients with obvious and severe disease, but it would be much less

accurate when used to detect mild or early disease.

In an accompanying commentary, Toshi Furukawa and Gordon Guyatt

underscore the importance of the study by Rutjes and colleagues. They

see diagnosis and test performance as proceeding in a stepwise

fashion, starting with a set of symptoms and signs. Knowing the

accuracy of a test in a real clinical setting is critical, as is

knowledge of the accuracy of the gold standard.

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