POS0241 VALIDATION OF THE ANKYLOSING SPONDYLITIS DISEASE ACTIVITY SCORE WITH A QUICK QUANTITATIVE C-REACTIVE PROTEIN ASSAY (ASDAS-QCRP) IN PATIENTS WITH AXIAL SPONDYLOARTHRITIS (AXSPA): A PROSPECTIVE, NATIONAL, MULTICENTER STUDY
Authors: F. Proft, J. Schally, H. C. Brandt, J. Brandt-Juergens, G. R. Burmester, H. Haibel, H. Käding, K. Karberg, S. Lüders, B. Muche, M. Protopopov, J. Rademacher, V. Rios Rodriguez, M. Torgutalp, M. Verba, S. Zinke, D. Poddubnyy
Journal: Annals of the Rheumatic Diseases (2021)

Background: According to international recommendations, the Ankylosing Spondylitis Disease Activity Score (ASDAS) is the preferred score for assessing disease activity in axial spondyloarthritis (axSpA) [1]. However, routine determination of C-reactive protein (CRP) to calculate ASDAS values takes hours to days. This limits the use of ASDAS in clinical routine and clinical trials and hinders the implementation of treat-to-target approaches in axSpA. Whereas quick quantitative CRP (qCRP) tests allow CRP assessment within a few minutes. In a pilot project the performance of qCRP-based ASDAS assessment (ASDAS-qCRP) was already investigated in a single center study of 50 newly diagnosed, bDMARD-naïve axSpA patients with promising results [2]. Objectives: To validate the ASDAS-qCRP in a prospective, multicenter study of axSpA patients in a typical axSpA cohort with an appropriate sample size. Methods: The study was conducted in five centers in Germany. Consecutive adult (≥ 18 years) axSpA patients were included. In addition to a rheumatological assessment, including patient reported outcomes (PROs), routine CRP and erythrocyte sedimentation rate (ESR) were measured in the local labs. Additionally, a qCRP testing with the „QuikRead go instrument“ (Aidian Oy, Finland) was performed at the study center (measurement range 0.5 - 200 mg/l for hematocrit concentrations of 40 – 45%). Statistical analysis included descriptive statistics, cross tabulation and weighted Cohen´s kappa comparing disease activity categories, Bland-Altman plots and intraclass correlation coefficient (ICC) for ASDAS-CRP and ASDAS-qCRP. Results: In this study 251 axSpA patients were included between January and September 2020 (mean age: 38.4 years; mean disease duration: 6.2 years, 159 patients (63.3%) were male, 211 (84.1%) HLA-B27 positive and 195 (77.7%) were classified as radiographic axSpA). 143 patients (57.0%) were treated with bDMARDs. CRP and qCRP showed mean values of 2.12 and 2.17 mg/l, respectively. With the ASDAS-qCRP, 242 patients (96.4%) were assigned to the same disease activity category as compared to the ASDAS based on the conventional lab CRP measurement (Table 1). Weighted Cohen´s kappa was 0.966 (95%CI: 0.943; 0.988). ICC for ASDAS-CRP- and ASDAS-qCRP-values was 0.997 (95%CI: 0.994; 0.999). The agreement of ASDAS-qCRP and ASDAS-CRP is shown in a Bland-Altman plot (Figure 1). Table 1. Disease activity categories by ASDAS-qCRP vs. ASDAS-CRP ASDAS-qCRP (n = 251) Inactive Disease (&lt; 1.3) Low Disease Activity (1.3 - &lt; 2.1) High Disease Activity (2.1 - 3.5) Very high Disease Activity (&gt; 3.5) ASDAS-CRP Inactive Disease (&lt; 1.3) 56 (22.3%) 2 (0.8%) Low Disease Activity (1.3 - &lt; 2.1) 62 (24.7%) 7 (2.8%) High Disease Activity (2.1 - 3.5) 97 (38.6%) Very high Disease Activity (&gt; 3.5) 27 (10.8%) The fields highlighted in red indicate that disease activity categories do not match. ASDAS = Ankylosing Spondylitis Disease Activity Score, CRP = C-reactive protein, qCRP = quick quantitative CRP Conclusion: The ASDAS-qCRP and ASDAS-CRP showed an almost perfect agreement on the assignment to disease activity categories (96%) with the important advantage of time. With ASDAS-qCRP, rheumatologists could base their clinical decision-making on a disease activity measurement by using a composite score immediately. ASDAS-qCRP, therefore, can be integrated in clinical routine and clinical trials in the future and may facilitate implementation of the treat-to-target concept in axial SpA. References: [1]Smolen JS, et al. Ann Rheum Dis. 2018 Jan; 77(1):3-17. [2]Proft F, et al. Joint Bone Spine. 2019 Jul 29. Figure 1. Bland-Altman plot for ASDAS-qCRP and ASDAS-CRP Acknowledgements: The authors would like to deeply thank Braun T, Doerwald C, Deter N, Höppner C, Lackinger J, Lorenz C, Lunkwitz K, Mandt B, Sron S and Zernicke J for their practical support and coordinating the study. Funding statement: The AQUA study was supported by an unrestricted research grant from Novartis. Testing kits were provided free of charge from Aidian Oy, Finland. Disclosure of Interests: None declared