A Primary Care Approach to the Use and Interpretation of Common Rheumatologic Tests

Abstract

The results of common rheumatologic laboratory tests play an important part in the diagnosis and management of rheumatic diseases. Rheumatologic test results can often be ambiguous and can sometimes be misleading, particularly in primary care settings. Because the diagnosis of most rheumatic conditions depends on information derived from sources other than serum tests, these laboratory values are usually supportive rather than diagnostic [1]. Few serum test results are pathognomonic for a specific rheumatic disease and alone are insufficient to determine a diagnosis [2]. Test results should be interpreted in a clinical context, which includes information derived from the history and physical examination, basic laboratory tests, radiographic and other imaging studies, and synovial fluid analysis. Serum rheumatologic tests are most useful for confirming a clinically suspected diagnosis. Because there is a high incidence of false-positive results in the general population, these tests have little clinical utility when there is a low pretest probability. Furthermore, the predictive value of serum rheumatologic tests is limited when performed in settings in which the prevalence of rheumatic conditions is low. Studies suggest that primary care physicians overuse common rheumatologic tests [3]. The practice of routinely ordering a battery of rheumatologic laboratory tests to ‘‘rule out’’ rheumatologic disease is not uncommon [1]. This approach rarely leads to a definitive diagnosis and