The other 13 were misclassified as not having vasculitis. Only half of the patients given a diagnosis of one of the four types of vasculitis criteria fit the appropriate set. Separate criteria are needed for classification and for diagnosis. In Rao and coworkers' patients, diagnosis of vasculitis was based on a physician's overall judgment after chart review rather than on predefined or standard criteria. The reader does not know, for example, which clinical or laboratory features led to the specific diagnosis in individual patients or whether physicians in other centers would agree with the diagnoses.
Standardized criteria based on analysis of a series of cases can answer such questions.
Multicenter studies help iron out regional or ethnic variations in disease and provide the numbers of cases needed to analyze uncommon diseases, such as vasculitis. Another, more general problem is the large number of diagnostic terms used in vasculitis. Rao and coworkers listed 14 different diagnoses in only 51 cases. Standardized criteria order our approaches to the study of disease cause, course, and therapy. They focus our objectives in clinical research and enhance the identification of important clinical differences and subsets of diseases.