This study aimed to determine amongst patients with axSpA factors associated with decreased spinal mobility. Also, to ascertain whether poor mobility is a predictor of response to anti‐TNFα therapy. A prospective UK cohort study of persons meeting ASAS criteria for axial spondyloarthritis. At recruitment, clinical and patient‐reported factors independently associated with spinal mobility were determined. Amongst those commencing anti‐TNFα therapy, factors that were independent predictors of response were determined using ASAS, quality of life, and ASDAS response criteria.

1,960 participants were eligible; 70% male, median age 48 years, median BASMI score 3.6. Factors independently associated with poor spinal mobility were: poorer function; meeting x‐ray criteria for AS; longer symptom duration; higher levels of inflammation (measured by CRP); older age; male gender; not being currently employed and lower levels of education. Poorer mobility was an independent predictor of not meeting response criteria for ASAS20 (OR per increasing score 0.80), ASAS40 (0.69), quality of life (β 0.64), but was not related to meeting ASDAS response criteria.

BASMI was estimated moderately well by other routinely measured factors in patients with axSpA and was an independent predictor of response to biologic therapy for some, but not all, commonly used measures. The consensus around its role in disease monitoring and clinical decisions, particularly in the likely context of face to face consultations becoming less frequent, remains to be established.