Objectives: To evaluate various validity aspects of four disease activity scores (ASDAS) for ankylosing spondylitis (AS) in comparison to the BASDAI, the individual components as well as physician and patient global assessment of disease activity.
Methods: The analyses were done in two different cohorts of AS patients: 1) the NOR-DMARD database including patients starting on a DMARD or TNF-blocker and 2) patients participating in double-blind placebo-controlled randomized clinical trials with TNF-blockers in four departments. Discrimination between patients in low versus high disease activity according to various definitions, and between various levels of change were analysed as standardized mean difference (difference of the group means divided by the pooled SD of the group means) and t-score.
Results: The 4 ASDAS are highly discriminatory in differentiating patients with different levels of disease activity and patients with different levels of change. The ASDAS scores outperform the BASDAI and single components in all settings: patient- or physician based, reflecting status or change, with normal or with elevated CRP, in the presence or absence of peripheral arthritis. There were no major differences between the four ASDAS scores. Based on feasibility the ASAS membership has selected the ASDAS including back pain, duration of morning stiffness, patient global, peripheral joints complaints and CRP as the preferred ASDAS.
Conclusions: The ASDAS is a validated, highly discriminatory instrument for assessing disease activity in AS including patient reported outcomes as well as CRP.