A simple enzyme immunoassay for the demonstration of rheumatoid factor

Abstract

An enzyme-linked immunosorbent assay (ELISA) for the demonstration of rheumatoid factor (RF) is described. Human IgG is used as antigen in the assay and the presence of RF is demonstrated by anti-human IgM conjugated to alkaline phosphatase. The assay is simple to perform and can be completed in one day. The recording of results is objective by means of a spectrophotometer, or alternatively the results can be read by the naked eye. There is good agreement between the RF-ELISA results and those obtained by the classical latex fixation and Waaler-Rose tests. All sera with a latex fixation titre ⩾ 128 and 70% (1420) of sera with a titre of 64 were positive in the RF-ELISA, whereas 17107 (16%) sera with titres between 4 and 32 were positive in the assay. 3 out of 70 (4%) Waaler-Rose positive sera gave negative results in the RF-ELISA. A positive RF-ELISA result was obtained in one out of 26 patients with non-specific arthritis studied. In 43 patients with a diagnosis of probable or definite rheumatoid arthritis, RF was detected in 27 cases (63%) by the RF-ELISA, whereas the classical tests detected RF in 21 cases (49%).