Acid Phosphatase Activity in the Synovial Fluid of Patients with Rheumatoid Arthritis and Other Joint Disorders

SummaryThe acid phosphatase activity was examined in the synovial fluid of a series of 155 patients with different joint disorders. Enzyme assay and electrophoretic examination on starch gel were performed with alpha-naphthyl phosphate as substrate. Patients with rheumatoid arthritis, showed significantly higher levels than those with bacterial arthritis, osteoarthritis and non-inflammatory joint effusions. About 70 per cent of the patients with RA had higher acid phosphatase activities than those found among the patients with non-rheumatoid diseases. Patients with chronic synovitis were found to represent a heterogeneous group, where those with low acid phosphatase activity recovered while those with a high activity frequently developed rheumatoid arthritis. Patients with bacterial arthritis had low acid phosphatase levels. The results indicate that determinations of the acid phosphatase activity in the synovial fluid may be valuable in the diagnosis of RA and in the prognosis of other joint effusions.