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Serum rheumatologic tests are generally most useful for confirming a clinically suspected diagnosis. Testing for rheumatoid factor is appropriate when rheumatoid arthritis, Sjogren's syndrome or cryoglobulinemia is suspected. Antinuclear antibody testing is highly sensitive for systemic lupus erythematosus and drug-induced lupus. Anti-double-stranded DNA antibodies correlate with lupus nephritis; the titer often corresponds with disease activity in systemic lupus erythematosus. Testing for anti-Ro (anti-SS-A) or anti-La (anti-SS-B) may help confirm the diagnosis of Sjogren's syndrome or systemic lupus erythematosus; these antibodies are associated with the extraglandular manifestations of Sjogren's syndrome. Cytoplasmic antineutrophil cytoplasmic antibody testing is highly sensitive and specific for Wegener's granulomatosis. Human leukocyte antigen-B27 is frequently present in ankylosing spondylitis and Reiter's syndrome, but the background presence of this antibody in white populations limits the value of testing. An elevated erythrocyte sedimentation rate (ESR) is a diagnostic criterion for polymyalgia rheumatica and temporal arteritis; however, specificity is quite low. ESR values tend to correlate with disease activity in rheumatoid arthritis and may be useful for monitoring therapeutic response. [ABSTRACT FROM AUTHOR]