[Basic principles of selection and use of diagnostic tests: practical applicability to individual patients]

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 the study's results about the test; 2) diagnostic properties of the test and 3) applicability of the test in clinical setting. The rational use and correct interpretation of diagnostic tests are based on these three factors. In two previous articles, we presented the basic principles concerning the validity of the results from the study that defined the specific test as well as the diagnostic properties of the tests. In this final article we discuss the applicability of the test to the individual patient in clinical practice.