The Sensitivity to Change of the ASAS Health Index in an Observational Real-Life Cohort Study

Objective The Assessment of Spondyloarthritis international Society Health Index (ASAS HI) measures global functioning and health in patients with axial spondyloarthritis (axSpA) covering domains of physical, emotional, and social functioning. The main aim of this study was to investigate the sensitivity to change of ASAS HI in comparison with established variables of disease activity, function, and mental health.

Methods Patients with axSpA from the disease register RABBIT-SpA with follow-up time of at least 12 months and available ASAS HI questionnaires were included. Patients received questionnaires addressing disease activity (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI], Ankylosing Spondylitis Disease Activity Score [ASDAS]), physical function (Bath Ankylosing Spondylitis Functional Index [BASFI]), mental health (5-item World Health Organization Well-Being Index [WHO-5]), and global functioning (ASAS HI). Standardized response means (SRMs) were calculated to compare the sensitivity to change of different variables.

Results Six hundred and sixty-seven patients were included, 552 treated with biologic disease-modifying antirheumatic drugs (bDMARDs) and 115 with conventional synthetic DMARDs and/or nonsteroidal antiinflammatory drugs (control group). Between baseline and month 12, the mean ASAS HI declined from 6.9 to 5.1 in the bDMARD group and from 5.9 to 5.6 in the conventionally treated group. In the bDMARD group, the SRM of ASAS HI was 0.52, compared to 0.59 for BASFI, 0.65 for WHO-5, 0.73 for BASDAI, and 0.90 for ASDAS. The following ASAS HI domains were most frequently affected: pain (78% agreed), maintaining body position (75%), and energy/drive (73%). In the patients receiving bDMARDs, there was an improvement in all items. In the control group, the largest improvement was seen in pain.

Conclusion As expected, ASDAS and BASDAI as disease activity scores showed high sensitivity to change, whereas changes in physical function (BASFI), mental health (WHO-5), and the broader concept of functioning and health (ASAS HI) were moderate.