Concise report Use of a 12-week observational period for predicting low disease activity at 52 weeks in RA patients treated with abatacept: a retrospective observational study based on data from a Japanese multicentre registry study

Objective. Only a few studies have assessed predictive factors for the long-term efficacy of abatacept. This study aimed to provide clinical evidence of an adequate observational period for predicting low disease activity (LDA) achievement at 52 weeks in RA patients treated with abatacept. Methods. Participants were all patients registered in a Japanese multicentre registry who were treated with abatacept and had at least 52 weeks of follow-up (n = 254). Results. Areas under the receiver operating characteristic curves for the 28-joint count with CRP (DAS28CRP) at each time point for LDA achievement at 52 weeks were: 0.686 (cut-off score: 4.6) at baseline, 0.780 (3.8) at 4 weeks, 0.875 (3.3) at 12 weeks, and 0.900 (3.0) at 24 weeks. Although patients with a DAS28-CRP score< 3.0 at 24 weeks had the highest proportion of LDA achievement at 52 weeks (79.3%), the proportion for those with a score< 3.3 at 12 weeks was comparable (77.2%, P = 0.697). Proportions were significantly lower in patients with a score< 3.8 at 4 weeks or<4.6 at baseline. Multivariate logistic regression demonstrated that a DAS28 score of< 3.3 at 12 weeks was an independent strong predictor for LDA at 52 weeks (adjusted odds ratio: 15.2, P< 0.001). Conclusion. Twelve weeks is an adequate observational period to judge the long-term clinical efficacy of abatacept, and is about as early as the period for assessing TNF blockade therapy.