The role of the laboratory in the evaluation of rheumatic diseases.

This article presents information on the role of immunologic laboratory tests in evaluating patients with rheumatic disease. The focus is on 3 commonly used tests: antinuclear antibodies, rheumatoid factor, and the erythrocyte sedimentation rate. Background data on various statistical principles that are key to interpretation of these tests are also discussed. The goal is to emphasize that improper use and interpretation of such test results can lead to incorrect diagnosis and unnecessary therapy, potentially putting the patient at risk. Thus, these tests should be ordered in the context of other clinical information that provides the practitioner with an accurate estimate of disease probability.