Rheumatoid Factor Variation Complicates RA Criteria

Uniform application of the 2010 American College of Rheumatology/European League Against Rheumatism criteria for rheumatoid arthritis (RA) is hampered by difficulty in defining a high rheumatoid factor (RF) level because of the variation in RF levels obtained with the use of different methods. The prognostic value of high RF level is limited compared with anti–cyclic citrullinated protein (anti-CCP) antibody positivity.

van der Linden and associates studied 972 patients in 3 cohorts for RA development and arthritis persistence. Test characteristics (eg, positive and negative likelihood ratios [LRs]) and absolute posttest changes in RA status (positive predictive value [PPV] and negative predictive value [NPV]) were determined.

The presence of anti-CCP antibody had a better balance between positive LR and negative LR and between PPV and NPV for RA development than high RF levels. Performing an anti-CCP antibody test in addition to RF level testing seemed more valuable than determining the RF level after determining the presence of anti-CCP antibodies. The association between anti-CCP antibodies and RA severity was stronger than that between high RF level and RA severity.

The authors noted that omitting RF level may improve the criteria.