Construct validity of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS) treatment target cut-offs in a BASDAI treat-to-target axial spondyloarthritis cohort: a cross-sectional study

Abstract

Objective

In axial spondyloarthritis (axSpA), the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS) are recommended for use in treat-to-target (T2T) strategies. However, BASDAI disease states may be a less suitable T2T instrument than ASDAS, since BASDAI contains non-disease activity related items. The objective of our study was to investigate the construct validity of BASDAI and ASDAS disease states.

Method

We performed a single-centre cross-sectional study on BASDAI and ASDAS construct validity in long-term BASDAI T2T-treated axSpA patients. Our hypothesis was that BASDAI is less representative of disease activity than ASDAS owing to the focus on pain and fatigue, and missing an objective item, e.g. C-reactive protein (CRP). This was operationalized using several subhypotheses.

Results

The study included 242 axSpA patients. BASDAI and ASDAS disease states showed a similar relation to Patient Acceptable Symptom State and T2T protocol adherence. The proportions of patients with high BASDAI and ASDAS disease activity fulfilling Central Sensitization Inventory and fibromyalgia syndrome criteria were similar. The correlation with fatigue was moderate for both BASDAI (Spearman’s rho 0.64) and ASDAS (Spearman’s rho 0.54) disease states. A high ASDAS was strongly correlated with increased CRP (relative risk 6.02, 95% CI 3.0–12.09), while this correlation was not seen for BASDAI (relative risk 1.13, 95% CI 0.74–1.74).

Conclusion

Our study showed moderate and comparable construct validity for BASDAI- and ASDAS-based disease activity states, with the expected exception of association with CRP. Therefore, no strong preference can be given for either measure, although the ASDAS seems marginally more valid.

Acknowledgement

We thank A Verkerk for data collection.

Disclosure statement

FvG is a member of the ASAS executive committee. AdB has received research grants (to the institution) from AbbVie, Amgen, Roche, Biogen, Lilly, Novartis, Sanofi, and Gilead. The remaining authors have no potential conflicts of interest to declare.

Author contributions

CM, TB, NdB, LV, and AdB were involved in the study design. CM was involved in the data collection. CM and TB performed the data analyses. All authors were involved in writing, revision, and final approval of the manuscript. CM is the study guarantor. CM contributed to all aspects of the study.

Data availability statement

The data underlying this article will be shared upon reasonable request to the corresponding author according to FAIR principles.

Ethics approval

This study was reviewed by the CMO region Arnhem-Nijmegen and was officially exempted from formal review (CMO number 2021-7431).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03009742.2023.2213509