This study evaluated the interaction of anticitrullinated protein antibody (ACPA) and rheumatoid factor (RF) in predicting sustained clinical response in an observational registry of patients with rheumatoid arthritis (RA) followed in routine practice.
Patients with RA enrolled in the Ontario Best Practices Research Initiative registry, with ≥1 swollen joint, autoantibody information and ≥1 follow-up assessment were included. Sustained clinical remission was defined as Clinical Disease Activity Index (CDAI) ≤2.8 in at least two sequential visits separated by 3–12 months. Time to sustained remission was assessed using cumulative incidence curves and multivariate cox regression.
Among 3251 patients in the registry, 970 were included, of whom 262 (27%) were ACPAneg/RFneg, 60 (6.2%) ACPApos /RFneg, 117 (12.1%) ACPAneg/RFpos and 531 (54.7%) ACPApos /RFpos at baseline. Significant between group differences were observed in age (p=0.02), CDAI (p=0.03), tender joint count (p=0.02) and Health Assessment Questionnaire (p=0.002), with ACPApos patients being youngest with lowest disease activity and disability. No difference in biologic use was found between groups (20.2% of patients).
Over a mean follow-up of 3 years, sustained remission was achieved by 43.5% of ACPApos/RFpos patients, 43.3% of ACPApos /RFneg patients, 31.6 % of ACPAneg/RFpos patients and 32.4% of ACPAneg/RFneg patients (p=0.01). Significant differences were observed in CDAI improvement based on ACPA and RF status where ACPApos/RFpos had a shorter time to achieving sustained remission (HR 1.30; 95% CI 1.01 to 1.67) and experienced significantly higher improvements compared with ACPAneg/RFneg patients.
Combined ACPA and RF positivity were associated with improved and faster response to antirheumatic medications in patients with RA.