Early intervention in rheumatoid arthritis (RA) reduces long-term disability. However, early diagnosis of RA can be difficult, as the disease may initially be indistinguishable from other forms of arthritis. Recent studies indicate that autoantibodies can be detected years before clinical symptoms develop. In a cohort with recent-onset arthritis, we aimed to assess the value of autoantibodies in predicting the development of RA in patients with undifferentiated arthritis (UA).

IgM rheumatoid factors (IgM-RF) and anti-cyclic citrullinated peptide (CCP) antibody tests were performed at baseline in 936 consecutive, newly referred patients with recent-onset arthritis. Two weeks after inclusion arthritis, patients who could not be properly classified were categorized as UA. Patients with UA were followed for 3 years and evaluated for progression to RA.

At 2 weeks, 346 of 936 patients (37%) with recent-onset arthritis were classified as having UA. After 3 years of follow-up, 127 UA patients (40%) had progressed to RA. However, RA had developed in 64 of 69 UA patients with a positive anti-CCP test, giving a positive predictive value (PPV) of 93% and a negative predictive value (NPV) of 74%. Progression to RA was observed in 51 of 68 UA patients with IgM-RF antibodies at baseline (PPV 75%, NPV 70%).

Up to 3 years before a diagnosis of RA was made, autoantibodies were detected in patients with UA. Detection of anti-CCP antibodies had a high predictive value for the progression to RA. Thus, screening for anti-CCP antibodies in UA allows physicians to predict progression to RA.