Rheumatoid Factor in Serum and Joint Fluid

Abstract

Ninety-six paired sera and joint fluids were examined by the latex fixation test. Thirty-one were strongly positive in both sera and joint fluid; patients from whom these specimens were taken all had definite or classic rheumatoid arthritis and eighteen of these had typical rheumatoid nodules. Thirty-six were negative in both sera and joint fluid; eight patients from whom these specimens were taken had definite or classic rheumatoid arthritis and three had rheumatoid nodules. The remaining twenty-nine pairs were either low titer positive in both specimens or low titer positive in one and negative in the other; seventeen of these patients had definite to classic rheumatoid arthritis and four had rheumatoid nodules. There were no instances of strongly positive serum and negative joint fluid. If the serum is positive by the latex test, the joint fluid is also positive and in slightly higher titer. This fact coupled with other evidence supports the hypothesis that rheumatoid factor is synthesized and released in connective tissue, probably moving to the serum via the lymphatics. Low titer positive tests occurred in several nonrheumatic diseases. Clinical indications for joint fluid latex tests and interpretation of positive tests in joint fluid is discussed.