Rheumatoid factor by laser nephelometry and Waaler–Rose assay: prognostic value in patients with recent‐onset rheumatoid arthritis

Abstract

Objective: To evaluate the prognostic value of rheumatoid factor (RF), detected in the Waaler–Rose agglutination assay and by nephelometry, in patients with recent‐onset rheumatoid arthritis (RA).Methods: Consecutive patients with new‐onset RA between 1993 and 1997 were followed for a median period of 4.7 years. Clinical data at baseline and drug use during the disease course were recorded. Outcome parameters studied were disease process, damage (erosions, joint surgery, extra‐articular manifestations, and new co‐morbidity), and death. Cut‐off levels for RF were >40 IU/mL (nephelometry) and titres ⩾1:160 (Waaler–Rose haemagglutination).Results: RF tests were negative by both methods in 22% of RA patients (RF− group), while 33% were RF positive by nephelometry only (RF+ group) and 45% were positive by Waaler–Rose and nephelometry (RF++ group). Baseline clinical and laboratory findings as well as the number of subsequently used disease‐modifying anti‐rheumatic drugs (DMARDs), the number of patients starting and the time spent on steroid therapy were similar in the three RF groups. Odd ratios for death (n = 23), erosions (n = 62), and serious extra‐articular disease manifestations (EAMs) (n = 13) as well as patient survival, erosion‐free or surgery‐free survival rates did not differ between the RF groups. Only rheumatoid nodules were more frequent in RF++ patients.Conclusion: The baseline presence of RF by either Waaler–Rose or nephelometry was not associated with differences in drug therapy, morbidity other than rheumatoid nodules, or mortality in RA patients in the first 5 years of disease. Being immunoglobulin M (IgM) RF positive thus had little impact on RA patient outcome.