Background: Improvement in functioning and health as assessed by the ASAS Health Index (HI) is an important outcome of interventions in patients with axial spondyloarthritis (axSpA). The ability of various ASAS HI thresholds to discriminate between treatment arms of an active comparator trial have been demonstrated recently by our group with absolute improvement in the ASAS HI in general being superior to relative changes [1, 2]. Objectives: To assess whether ASAS HI response measures (absolute improvement of ≥3.0 and relative improvement of ≥30%) and reaching a status of good global functioning (ASAS HI ≤5.0) adequately discriminate between the changes and states in relevant external outcomes. Methods: In this post-hoc analysis from the tight-controlled, treat-to-target (T2T) trial TICOSPA (2), data of active axSpA patients randomized to either the T2T arm (visits every 4 weeks, prespecified strategy of treatment intensification until achieving low disease activity) or usual care (UC; visits every 12 weeks, treatment at the rheumatologist's discretion) were used. The performance of ASAS HI response-and status scores against change (ASAS-40/ BASDAI-50 response, change in patient global/ BASDAI, and ASDAS improvement) and external status scores (ASAS partial remission, ASDAS status) was assessed, respectively. Analysis were performed by comparing the mean values and proportion of responses of continuous and dichotomous response outcomes, by t-tests. Missing data on outcomes was handled by non-responder imputation (NRI). Results: ASAS HI was available in 160 patients, both at baseline and at week 48. At w48, an ASAS HI improvement of ≥30%, improvement of ≥3 points and ASAS HI ≤5.0 was achieved by 56 (35%), 51 (31.9%) and 54 (33.7%) patients, respectively. Patients with a meaningful improvement in global functioning had a larger reduction in patient global and disease activity as well a greater chance to reach remission compared to patients with no significant improvement in global functioning (Table 1). Health ...