The predictability of ASDAS on drug survival in patients with ankylosing spondylitis on biologic therapy: data from the KOBIO registry

BACKGROUND: The Ankylosing Spondylitis (AS) Disease Activity Score (ASDAS) is largely used for assessing disease activity in patients with AS. OBJECTIVES: We aimed to investigate the predictability of ASDAS on drug survival in patients with low Bath AS Disease Activity Index (BASDAI) during biologic therapy. DESIGN: Using data from multi-center, prospective, observational prospective cohort, Korean College of Rheumatology Biologics and Targeted Therapy (KOBIO) registry. METHODS: The study population consisted of patients enrolled in the KOBIO registry from December 2012 to December 2018. The baseline demographic data and variables such as extra-articular manifestations, HLA-B27 positivity, family history of spondyloarthritis, ASDAS C-reactive protein (CRP), BASDAI, and Bath AS Functional Index scores were collected from the database. The disease activity indices were followed yearly after initiating a tumor necrosis factor (TNF) inhibitor (TNFi). Disease activities were defined as high (ASDAS-CRP ⩾ 2.1, BASDAI ⩾ 4) and low (ASDAS-CRP < 2.1, BASDAI < 4). RESULTS: Data from 1773 patients were analyzed. Among 269 patients with low BASDAI at baseline, 151 (56.1%) patients had high ASDAS-CRP, yet in 142 patients with low ASDAS-CRP at baseline, only 24 (16.9%) patients had a high BASDAI. High ASDAS-CRP captured more patients who had initiated or switched to a TNFi than those with high BASDAI (92.5% versus 84.8%, respectively, p < 0.001). Moreover, among AS patients with low BASDAI after 1 year of therapy, drug persistence in the following year was significantly lower in patients with high ASDAS than in those with low ASDAS (68.7% versus 82.5%, p < 0.001). CONCLUSION: ASDAS-CRP not only has its advantages over BASDAI in assessing disease activity but also low ASDAS-CRP at 1 year can be a marker of long-term drug survival of TNFi therapy.