How to appraise a diagnostic test

Abstract

Urologists frequently encounter problems in making a clinical diagnosis whose resolution requires the use of diagnostic tests. With an ever increasing choice of investigations being available, the urologist often has to decide which diagnostic test(s) will best resolve the patient's diagnostic problem. In this article, we aim to help the urologist understand how to critically appraise studies on diagnostic tests and make a rational choice. This article presents the guiding principles in scientifically assessing studies on diagnostic tests by proposing a clinical scenario. The authors describe a standardized protocol to assess the validity of the test and its relevance to the clinical problem that can help the urologist in decision making. The three important issues to be considered when evaluating the validity of the study are to identify how the study population was chosen, how the test was performed and whether there is a comparison to the gold standard test so as to confirm or refute the diagnosis. Then, the urologist would need to know the probability of the test in providing the correct diagnosis in an individual patient in order to decide about its utility in solving the diagnostic dilemma. By performing the steps described in this article, the urologist would be able to critically appraise diagnostic studies and draw meaningful conclusions about the investigations in terms of validity, results and its applicability to the patient's problem. This would provide a scientific basis for using diagnostic tests for improving patient care.

Keywords: Critical appraisal; diagnostic study; evidence-based medicine; likelihood ratio; user guide.

Figure 1

The Fagan nomogram[23] [reproduced with permission from The Massachusetts Medical Society; copyright^© (1975) Massachusetts Medical Society; all rights reserved]