POS0344 BASDAI CUT-OFFS FOR DISEASE ACTIVITY CORRESPONDING TO ASDAS-ESR CUT-OFFS IN AXIAL SPONDYLARTHRITIS – RESULTS FROM THE EUROSPA COLLABORATION

Background
The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is often used for classifying patients according to disease activity states. BASDAI values of 2, 4 and 6 have been applied as cut-offs for inactive disease (ID), between low disease activity (LDA) and high disease activity (HDA) and for very high disease activity (VHDA), respectively, although these cut-off values have not been validated.
Objectives
We aimed to (i) identify BASDAI cut-offs for disease activity states corresponding to the Ankylosing Spondylitis Disease Activity Score (ASDAS) cut-offs, and (ii) investigate the impact of gender on the BASDAI cut-offs.
Methods
Prospectively collected real-world data from axSpA patients receiving tumour necrosis factor inhibitors (TNFi) from countries participating in the European Spondyloarthritis (EuroSpA) Research Collaboration Network were analysed [1]. We chose the ASDAS version based on erythrocyte sedimentation rate (ASDAS-ESR) for which the cut-offs were first developed [2]. Hence, data from 10 registries in EuroSpA with available BASDAI and ASDAS-ESR were included. Analyses were restricted to patients' first TNFi series with available data. To have the best representation of the disease activity states, follow-up data (6, 12 or 24 months) were used to select the cut-offs for ID and between LDA and HDA, while baseline data were used to select the cut-off for VHDA. We performed receiver operating characteristic (ROC) analyses to determine the optimal BASDAI values corresponding to ASDAS-ESR cut-offs using the Youden index (=sensitivity+specificity-1). Furthermore, we carried out separate ROC analyses to identify gender-specific BASDAI cut-offs. Finally, the level of agreement between the new BASDAI cut-offs and the ASDAS-ESR cut-offs was assessed.
Results
We included 4,672 axSpA patients (2,775 (59%) men) with a registration of both BASDAI and ASDAS-ESR at baseline and at least one follow-up visit. Mean (SD) BASDAI and ASDAS-ESR were 5.7 (2.1) and 3.3 (1.0) at baseline, and 3.0 (2.3) and 1.9 (1.0) at follow-up, respectively. The optimal BASDAI values corresponding to ASDAS-ESR 1.3, 2.1 and 3.5 were 2.1, 3.3 and 6.3, respectively (Figure 1). When comparing the BASDAI and ASDAS-ESR cut-offs, the level of agreement was lower for the VHDA cut-off compared to the other disease activity states (Table 1). The gender-specific BASDAI cut-offs corresponding to ASDAS-ESR cut-offs (i.e., 1.3, 2.1 and 3.5) were 2.1, 3.1 and 6.2 for men and 2.1, 3.3 and 6.4 for women, respectively (Figure 1). We also observed that fewer women met the ID and LDA cut-offs of <1.3 and <2.1 than men (Table 1).
Conclusion
The BASDAI cut-offs corresponding to ASDAS-ESR 1.3, 2.1 and 3.5 were 2.1, 3.3 and 6.3, respectively. There was no evidence of a clinically relevant difference in BASDAI cut-offs between men and women.