Basic principles on selection and use of diagnostic tests: properties of diagnostic tests

In clinical practice, in order to design and implement a specific therapeutic plan, as well as communicating an appropriate prognosis, the doctor needs to establish a precise diagnosis of the condition. Sometimes all one needs is a clinical impression. More often, however, the definition of an accurate diagnosis will mandate the interpretation of specific diagnostic tests as well. The rational use of diagnostic tests in cardiology--whether laboratorial or imaging--should be based on three factors: 1) validity of results of studies on the test; 2) diagnostic properties of the test; and 3) applicability of the test in the clinical setting. The rational use and the correct interpretation of diagnostic tests are based on these three factors. In a previous article we presented the basic principles concerning the validity of the results from the study that defined the specific test, and what level of evidence that constitutes. In this article we present the diagnostic properties of tests (sensitivity, specificity, positive and negative predictive values, likelihood ratios, odds). Finally, in a forthcoming paper we will discuss the applicability of the test in clinical cardiological practice.