The mucin clot test and the synovial fluid rheumatoid factor as diagnostic criteria in rheumatoid arthritis.

We evaluated the diagnostic usefulness of 2 synovial fluid (SF) tests viz the mucin clot test (MCT) and the rheumatoid factor (RF) test in rheumatoid arthritis (RA). SF was obtained from 140 patients, 60 with RA, 80 with other articular diseases. The sensitivity and specificity of the MCT in RA were 76% and 49%, respectively; the positive and negative predictive values (PPV, NPV) were 52% and 73%. The sensitivity and specificity of SF RF were 63% and 91% respectively compared with corresponding values of 75% and 87% for serum RF; PPV and NPV were 89% and 69%, and differed little from values obtained for serum RF. Our results suggest that RA diagnostic criteria should be revised to exclude the MCT, and that the detection of RF in SF in addition to its determination in serum is unnecessary in establishing a diagnosis of RA.