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Diagnostic Tests in Rheumatic Disease

Rheumatic disease often presents with a heterogeneity of clinical symptoms and a lack of specific clinical findings, including diagnostic tests; there is rarely a gold standard on which to rely. Each year, 15% of the American population will see a physician for musculoskeletal complaints associated with systemic lupus erythematosus and rheumatic disease.

Diagnostic Tests Rheumatic Disease and Systemic Lupus Erythematosus

No definitive diagnosis can be made through blood tests or other non-invasive evaluation; serologic markers of autoimmunity and are no match for a thorough clinical evaluation including history, physical examination and routine diagnostic evaluation. Invasive testing, such as tissue biopsy, is often non-diagnostic in patients with suspected rheumatic disease. It is not rare for patients with suspected or even documented rheumatic disease to develop non-rheumatic problems (eg, the patient with lupus who develops subacute bacterial endocarditis).

Erythrocyte Sedimentation Rate (ESR)

The ESR is a highly sensitive but nonspecific measure of "bodywide" inflammation. It is determined largely by fibrinogen and is among a large group of acute phase reactants that include C-reactive protein (CRP), ferritin, and haptoglobin. Among the rheumatic diseases, the sensitivity of this test is highest (90 to 99%) in polymyalgia rheumatica and temporal arteritis, perhaps in part because the ESR is one of the findings used to clinically define these diseases. Otherwise, the test is either less sensitive, inadequately studied or both. The ESR is often elevated in RA, systemic lupus erythematosus (SLE), various vasculitic disorders or gout, but a normal or only moderately elevated test is not useful to "rule out" these disorders. Conversely, an elevated ESR in RA may be due to infection or some other unrelated process, and the ESR rises with age (to approximately age divided by two). Thus, the test is not specific enough to be highly useful in clinical practice. Finally, some patients are found to have markedly elevated ESRs without a clear reason; in such circumstances, if a detailed history and physical examination do not point to an underlying explanation, only a modest evaluation (including routine malignancy screens, PPD, SPEP, chest x-ray, complete blood count, and tests of renal and liver function).