Laboratory Findings in the Patients with Arthritis

Arthritis is caused by various diseases including rheumatoid arthritis (RA), osteoarthritis, gout and trauma, and joint involvement also occurs in some autoimmune diseases, such as systemic lupus erythematosus and Sj$\ddot{o}$gren's syndrome. Some laboratory tests provide useful information in both diagnosis and prognosis. RF and anti-CCP (cyclic citrullinated peptide) antibody are detected in approximately 70-80% of patients with RA, and often associated with a worse prognosis (e.g., bony erosion and joint deformity). Acute phase reactants, such as erythrocyte sedimentation rate and C-reactive protein, parallel the activity of RA, and their persistent elevation are also associated with a poor prognosis. Crystal examination in synovial fluid is essential to confirm the diagnosis of gout and pseudogout, and the synovial fluid culture is also important in septic arthritis. Anti-nuclear antibody helps to distinguish non-immune arthritis from systemic rheumatic diseases. However, arthritis cannot be diagnosed only with laboratory findings, and physician should consider comprehensive physical examination, clinical findings, and imaging findings as well as laboratory findings. In this topic review, laboratory tests useful for diagnosis of arthritis will be discussed and summarized.

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