The use and misuse of classification and diagnostic criteria for complex diseases

Disease classification systems often perform poorly when they are used in the diagnosis of individual patients. A study of the diagnostic accuracy of the American Academy of Rheumatology classification criteria for several forms of vasculitis confirmed this. In diseases which occur infrequently, classification criteria may incorrectly identify patients who do not have the condition, known as a false-positive diagnosis. The inflammatory blood vessel diseases known as vasculitis occur with low enough frequency that the classification criteria do not perform well diagnostically.