[The diagnostic specificity and sensitivity and the importance of disease prevalence]

In this paper the terms "diagnostic specificity, sensitivity and efficiency" are explained using the example of feline immunodeficiency virus (FIV). Clinical conditions are discussed which require tests with high sensitivity and/or specificity. In addition it is shown that the prevalence of a disease is an important factor for the predictive value of a test result. For instance, tests with good specificity will lead to a high proportion of false negative values if the prevalence of the disease detected by the test is low. In order to improve the predictive value of a positive test result, the clinician must try to assign a patient to a population of individuals in which the prevalence of the suspected disease is elevated. This can be done by carefully evaluating the history and the clinical signs.