A comparison of the clinical usefulness of eight tests for IgM rheumatoid factor

The clinical usefulness of seven commercially available tests for IgM rheumatoid factor are compared using sera from 28 patients with classical rheumatoid arthritis with 126 patients from appropriate control groups. The test system which provided the greatest sensitivity and specificity for the diagnosis of rheumatoid arthritis was considered the most desirable. No attempt was made to test reproducibility. The Ortho latex slide screening test demonstrated the best balance of sensitivity and specificity with 24/28 positive in sera from patients with classical rheumatoid arthritis, and 6/127 positive in non-rheumatoid controls. Of the systems tested, the Behring latex test was least useful due to an unacceptable lack of sensitivity, with only 8/28 positive using sera from patients with classical rheumatoid arthritis. Until a more internationally standardized rheumatoid factor assay is available, the comparative results of this study may serve as a guide to clinicians and laboratory directors in selecting a clinical useful, commercially available test system.