Interpretation of synovial fluid data.

The routine battery of tests for synovial fluid analysis includes culture and Gram staining, polarizing microscopy, and total WBC and differential counts. If the volume of fluid collected is low, culture and polarizing microscopy have highest priority. Synovial fluid data are diagnostic in only two diseases: septic arthritis and crystal-induced arthritis. In traumatic arthritis, degenerative joint disease, rheumatoid arthritis, and systemic lupus erythematosus, synovial fluid data may provide evidence supporting the diagnosis.