In the past few years, several novel autoantibodies (autoAbs) have been described in patients with rheumatoid arthritis (RA), including an autoAb to citrullinated antigens (anti-CCP) and anti-RA33 autoAb. It was our aim to assess the value of these two autoAbs in relation to rheumatoid factor (RF) in discriminating RA from non-RA in a cohort of patients with very early arthritis.
Ninety-four patients with arthritis of less than 3 months' duration were included in this prospective study. Follow-up was for at least 1 year. Sixty-one patients had a final diagnosis of RA and 33 had other arthritides. Among the RA patients, RF was present in 34 (56%), anti-CCP in 18 (30%), and anti-RA33 in 15 (25%) at their first visit. Among the 33 non-RA patients, 6 were RF-positive, 3 had anti-RA33, and 1 had anti-CCP. Thus, anti-CCP was very specific for RA with a positive predictive value (PPV) of 95%, while RF and anti-RA33 were somewhat less specific, with PPVs of 85% and 83%, respectively. However, the co-occurrence of anti-RA33 and RF was observed exclusively in RA patients and thus had a PPV of 100% in this relatively small cohort of patients. In conclusion, these data suggest that the determination of autoantibodies such as anti-CCP and anti-A2/RA33 in addition to RF may be quite helpful in the early diagnosis of RA.