RT Journal Article SR Electronic T1 Arthritis development in patients with arthralgia is strongly associated with anti-citrullinated protein antibody status: a prospective cohort study JF Annals of the Rheumatic Diseases JO Ann Rheum Dis FD BMJ Publishing Group Ltd and European League Against Rheumatism SP 490 OP 494 DO 10.1136/ard.2008.105759 VO 69 IS 3 A1 W H Bos A1 G J Wolbink A1 M Boers A1 G J Tijhuis A1 N de Vries A1 I E van der Horst-Bruinsma A1 P P Tak A1 R J van de Stadt A1 C J van der Laken A1 B A C Dijkmans A1 D van Schaardenburg YR 2010 UL http://ard.bmj.com/content/69/3/490.abstract AB Background Anti-citrullinated protein antibodies (ACPA) are associated with increased risk for rheumatoid arthritis. Objective To investigate the effect of the presence and levels of ACPA on arthritis development in patients with arthralgia. Methods Patients with arthralgia positive for ACPA or IgM rheumatoid factor (IgM-RF) were tested for the shared epitope (SE) and were prospectively followed up for at least 12 months. Absence of clinical arthritis at inclusion and arthritis development during follow-up were independently confirmed by two investigators. Cox regression hazard analyses were used to calculate hazard ratios (HRs) for arthritis development. Results 147 patients with arthralgia were included (50 ACPA positive, 52 IgM-RF positive and 45 positive for both antibodies). After a median follow-up of 28 months (interquartile range (IQR) 19–39), 29 patients developed arthritis in a median of 4 (IQR 3–6) joints and 26 (90%) of these were ACPA positive. The presence of ACPA (HR = 6.0; 95% confidence interval (95% CI) 1.8 to 19.8; p = 0.004), but not of IgM-RF (HR = 1.4, 95% CI 0.6 to 3.1) nor the SE (HR = 1.5, 95% CI 0.7 to 3.0), was associated with arthritis development. Within the group of ACPA-positive patients, the risk for arthritis was enhanced by the presence of IgM-RF (HR = 3.0; 95% CI 1.4 to 6.9; p = 0.01) and high ACPA levels (HR = 1.7; 95% CI 1.1 to 2.5; p = 0.008), but not the SE (HR = 1.0; 95% CI 0.5 to 2.1; p = 1.0). Conclusion In patients with arthralgia the presence of ACPA (but not of IgM-RF or SE) predicts arthritis development. The risk in ACPA-positive patients may be further increased by the concomitant presence of IgM-RF or high levels of ACPA.