Background/Purpose: When assessing disease activity in patients with axial spondyloarthritis (axSpA), the Ankylosing Spondylitis Disease Activity Score with C-reactive protein (ASDAS-CRP) is recommended over ASDAS with erythrocyte sedimentation rate (ASDAS-ESR). Although ASDAS-CRP and ASDAS-ESR are not interchangeable, the same cut-offs are used to classify patients into four distinct disease activity states: inactive disease (ID), low disease activity (LDA), high disease activity (HDA) and very high disease activity (VHDA). These cut-offs were developed based on ASDAS-CRP. We aimed to (i) estimate optimal ASDAS-ESR values corresponding to the established ASDAS-CRP cut-offs (< 1.3, < 2.1 and > 3.5), and (ii) investigate the improvement of level of agreement between ASDAS-ESR and ASDAS-CRP disease activity states when applying the estimated ASDAS-ESR cut-offs.

Methods: Prospectively collected real-world data from axSpA patients starting a 1st, 2nd or 3rd tumor necrosis factor inhibitor (TNFi) from 9 countries participating in the European Spondyloarthritis (EuroSpA) Research Collaboration Network were analysed. Data were collected at baseline and three follow-up visits (6, 12 and 24 months) per TNFi treatment course. To have the best representation of the disease activity states, aggregated follow-up data were used to evaluate the ASDAS-CRP cut-offs for ID and between LDA and HDA, while baseline data were used to assess the cut-off for VHDA. We performed receiver operating characteristic analyses using the Youden index to estimate the optimal ASDAS-ESR values corresponding to ASDAS-CRP cut-offs. The level of agreement between ASDAS-ESR and ASDAS-CRP disease activity states was also assessed.

Results: We analysed data from 4,306 patients with complete registration of ASDAS scores at baseline and at least one complete follow-up registration of ASDAS scores during the same TNFi treatment course. Mean (SD) ASDAS-CRP and ASDAS-ESR were 3.5 (1.0) and 2.0 (1.0) at baseline and 3.3 (1.0) and 1.9 (1.0) at follow-up, respectively. The estimated ASDAS-ESR cut-offs between ID and LDA, between LDA and HDA and between HDA and VHDA corresponding to ASDAS-CRP cut-offs were < 1.4, < 1.9 and > 3.3, respectively (Table 1). Good agreement was observed between disease activity states applying the established ASDAS-ESR and ASDAS-CRP cut-offs, although the VHDA cut-off showed slightly worse agreement than the other two cut-offs (Table 2, upper panel). The statistical measures comparing the estimated ASDAS-ESR (< 1.4, < 1.9 and > 3.3) and ASDAS-CRP (< 1.3, < 2.1 and > 3.5) cut-off values performed slightly better only for VHDA as compared to applying the same cut-offs for both ASDAS versions (Table 2, lower panel). However, the proportion of discordance for the cut-offs for ID and between LDA and HDA increased slightly with the estimated ASDAS-ESR cut-off values.

Conclusion: In a multi-national cohort, the estimated ASDAS-ESR cut-offs between disease activity states were < 1.4, < 1.9 and > 3.3. The original cut-offs overall performed similarly as the ones we estimated. Our findings did not provide sufficient evidence to reject the established ASDAS-ESR cut-offs.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/which-asdas-esr-cut-offs-for-disease-activity-correspond-to-asdas-crp-cut-offs-in-axial-spondyloarthritis-results-from-the-eurospa-collaboration/