The use of ASDAS to evaluate disease activity and response to treatment in patients with axial spondyloarthritis starting the first biological drug: Are ASAS recommendations being followed?

Objectives: To determine the proportion of patients with axial spondyloarthritis (axSpA) who had ASDAS calculated at baseline and at least once within two follow-up visits after starting their first bDMARD; and to evaluate the likelihood of meeting ASAS criteria for treatment continuation at 3 and 6 months. Methods: Patients with axSpA from the Reuma.pt registry who initiated their first bDMARD and attended baseline, 3-month (3 M), and 6-month (6 M) visits were included. Availability of ASDAS at baseline was cross-tabulated with its availability in ≥1 follow-up visit. When ASDAS was absent, the use of alternative outcome measures was evaluated. Treatment response (∆ASDAS ≥1.1) at 3 M and 6 M was analyzed across four response patterns: no response, 3 M only, 6 M only, or both. Results: A total of 666 patients were included. Most had ASDAS at baseline (N = 540; 81 %), and 493 (74 %) also had ASDAS at 3 M and/or 6 M. No alternative outcome measure was predominantly used when ASDAS was absent. Among 336 patients with complete ASDAS evaluation, 58 % met ASAS continuation criteria at 3 M and 60 % at 6 M, with 86 % of response maintenance between 3 M and 6 M. Additionally, 25 % of 147 non-responders at 3 M responded at 6 M. Responders at both timepoints were more often male (65 % vs 45 %) and younger (mean age 35 vs 38 years). Conclusion: ASDAS is widely assessed in axSpA patients starting bDMARDs by Portuguese rheumatologists. Most patients respond within 3 months but waiting until 6 months to determine treatment continuation is reasonable.