Matched specimens of synovial fluid and serum from 141 patients with various types of synovitis were analyzed utilizing a group of standard immunologic tests. The results were correlated with the patients' clinical diagnoses.

Rheumatoid factors in synovial fluid and serum were detected by both the latex fixation test and the sensitized sheep cell agglutination test. The latex fixation test was more sensitive and detected rheumatoid factor in the joint fluid of some of the non-rheumatoid patients. The sensitized sheep cell agglutination test was a less sensitive, but more specific test for rheumatoid factor in the joint fluid of patients with rheumatoid arthritis.

Antinuclear antibodies were found most frequently in the synovial fluid and serum of patients with systemic lupus erythematosus. They were also present in 21 per cent of the rheumatoid synovial fluids and in 28 per cent of the rheumatoid serums, but were rarely detected in the synovial fluid or serum of patients with other conditions. Intracellular inclusions were present more frequently in synovial fluid leukocytes of patients with rheumatoid arthritis, but were detected in a few of the synovial effusions produced by a wide variety of other diseases.

A consistent relationship was noted between the total complement in synovial fluid and that in serum. Both values were low in patients with systemic lupus erythematosus. In rheumatoid patients only the synovial fluid levels were low. In patients with other diseases the synovial fluid had much higher complement levels which approached the serum complement values within the normal range.

The ratios of synovial fluid immunoglobulin to serum immunoglobulin for the three major classes (IgG, IgA, 1gM) were higher in rheumatoid patients, while patients with Reiter's syndrome showed the highest ratios for IgA and 1gM.

In addition to these specialized tests, synovial fluid analysis should include the routine tests to determine the presence of inflammation. Specific analysis for crystals and infectious organisms must always be performed as these results are pathognomonic of specific disease.

It is therefore concluded that a careful history, physical examination and roentgenographic evaluation supplemented by synovial fluid analysis which includes serologic tests will allow greater diagnostic accuracy in evaluating diseased or traumatized joints.