Synovial Fluid Complement: Usefulness in Diagnosis and Classification of Rheumatoid Arthritis

The relation between synovial fluid complement concentration and severity or prognosis of disease was studied in 62 patients with rheumatoid arthritis who were divided into 4 groups, on the basis of presence or absence of rheumatoid factor and low or normal synovial fluid complement concentration levels. The groups were similar with respect to various important criteria. Assessment of the disease by functional criteria, roentgenograms, synovial fluid polymorphonuclear leukocyte count, and synovitis showed more pronounced abnormalities in those patients with low synovial fluid complement levels or rheumatoid factor. Rheumatoid nodule formation correlated best with synovial fluid complement depletion. Low synovial fluid complement or rheumatoid factor, or both, is associated with severer disease and probably a poorer prognosis. Synovial fluid complement determination seems to be most useful in evaluation of patients with seronegative rheumatoid arthritis.