The occurrence of rheumatoid factor in synovial fluid

The concentration of gamma globulin and the latex agglutination reaction of synovial fluid have been compared to serum values in eighty-three patients with various forms of rheumatic disease. In the majority of patients with active rheumatoid arthritis and a positive agglutination reaction in serum, the reaction of synovial fluid also was positive, usually in a somewhat lower titer. This discrepancy may be related to the lower protein content of synovial fluid compared to serum. There were a number of cases, however, in which the agglutination reaction of synovial fluid was negative despite strongly positive agglutination reactions of the serum. It is possible that in some cases this may have been the result of recent intra-articular steroid treatment. There were several patients with suspected (possible or probable) rheumatoid arthritis in whom the agglutination reactions of the serum were negative and of the synovial fluid positive. The course of these subjects must be carefully followed before any conclusions can be drawn concerning the possible value of this observation in the early diagnosis of rheumatoid arthritis. This finding is compatible, however, with the belief that production of the rheumatoid factor in such cases may be confined to the tissues of one or a few joints. The synovial fluid from a small group of patients with a variety of other rheumatic diseases showed negative reactions with the exception of two patients with ankylosing spondylitis and peripheral arthritis. The study of synovial fluid samples, which have a strong positive agglutination reaction, by means of immunoelectrophoresis and ultra-centrifugationand the effects of mercaptoethanol treatment indicate that the factor responsible for latex agglutination is a macroglobulin.