Abstract
Objective Monitoring axial spondyloarthritis (axSpA) disease activity using validated indices (eg, Bath Ankylosing Spondylitis Disease Activity Index [BASDAI], Axial Spondyloarthritis Disease Activity Score [ASDAS]) is widely recommended but rarely followed in practice. The reasons, although varied, may be found in the scarcity of studies comparing the performance of these indices in daily practice. Here, we compare the performance of disease activity indices in clinical practice.
Methods This was an observational cross-sectional study involving 330 patients. The BASDAI, ASDAS, Bath Ankylosing Spondylitis Functional Index (BASFI), and Assessment of SpondyloArthritis international Society Health Index (ASAS HI) indices were included. Their correlations, degree of concordance, and discriminating capacity for different levels of disease activity and impact were compared using the appropriate statistics.
Results A total of 127 women (38.5%) and 203 men (61.5%) were included, with a mean age of 47.6 (SD 12.9) years and median disease duration of 8 (IQR 4-16) years. At inclusion, 209 patients (63.3%) were receiving biologic therapies, mostly tumor necrosis factor inhibitors. All measurement indices were highly correlated (Pearson r ≥ 0.73). Concordance between instruments was substantial, both with regard to the different activity thresholds and the different disease impact categories (κ ≥ 0.61). BASDAI cutoffs of 3.95 (area under the receiver-operating characteristic curve [AUC] 0.90) and 5.85 (AUC 0.90) accurately identified the ASDAS high and very high activity categories, respectively. An ASDAS ≥ 2.1 (AUC 0.87) and a BASDAI ≥ 3 (AUC 0.92) accurately discriminated the ASAS HI high impact category. Regardless of systemic therapy use, there was substantial agreement between BASDAI remission (≤ 2) and ASDAS inactive disease (< 1.3).
Conclusion The metrological performance of standard disease activity indices in axSpA were similar. The BASDAI values that identify the ASDAS categories are novel. We suggest using these indices interchangeably in routine clinical practice.