Laboratory tests to assess patients with rheumatoid arthritis: advantages and limitations.

Laboratory tests provide the most definitive information for diagnosing and managing many diseases, and most patients look to laboratory tests as the most important information from a medical visit. Most patients who have rheumatoid arthritis (RA) have a positive test for rheumatoid factor and anticyclic citrullinated peptide (anti-CCP) antibodies, as well as an elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). More than 30% 40% of patients with RA, however, have negative tests for rheumatoid factor or anti-CCP antibodies or a normal ESR or CRP. More than 30% of patients with RA, however, have negative tests for rheumatoid factor or anti-CCP antibodies, and 40% have a normal ESR or CRP. These observations indicate that, although they can be helpful to monitor certain patients, laboratory measures cannot serve as a gold standard for diagnosis and management in all individual patients with RA or any rheumatic disease. Physicians and patients would benefit from an improved understanding of the limitations of laboratory tests in diagnosis and management of patients with RA.