Estimating the Predictive Value Of a Diagnostic Test: How To Prevent Misleading or Confusing Results

The diagnostic process consists of a series of steps in which the estimated probability of particular disease is increased or decreased until either treatment can be instituted or the diagnosis excluded. The history and physical exam play an important role. If a therapeutic decision cannot confidently be made on clinical grounds alone, a diagnostic test may confirm or exclude a diagnosis or clearly indicate the need for further testing. An inappropriately chosen test or misinterpreted test result, however, may mislead the clinician and possibly harm the patient or simply be wasteful. Estimating the predictive values of a diagnostic test will help to avoid these pitfalls. This article shows the clinician a simplified way to do this.