[Basic principles of selection and use of diagnostic tests: analysis of the results of diagnostic studies]

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 need the interpretation of specific diagnostic tests as well. The rational use of diagnostic tests in cardiology--whether laboratorial or imagiologic--should be based on three factors: 1) validity of the study results about the test; 2) diagnostic properties of the test and 3) applicability of the test in the clinical setting. The rational use and correct interpretation of diagnostic tests are based on these three factors. In this article we present the basic principles concerning the validity of the results from the study that defined the specific test, and what level of evidence that constitutes. Other articles will address diagnostic properties of tests (sensitivity, specificity, positive and negative predictive values, likelihood ratios) as well as the applicability of the test in clinical practice.