Validation of the ASDAS with a quick quantitative CRP assay (ASDAS-Q) in patients with axial SpA: a prospective multicentre cross-sectional study

Abstract

Objectives: The objective of the study was to validate the Ankylosing Spondylitis Disease Activity Score (ASDAS) based on a quick quantitative C-reactive protein (qCRP) assay (ASDAS-Q) in a multicentre, prospective, cross-sectional study in patients with axial spondyloarthritis (axial SpA). Methods: Disease activity assessment was performed in prospectively recruited patients with axial SpA. Routine laboratory CRP was determined in the central laboratory of each study centre, while quick qCRP and erythrocyte sedimentation rate (ESR) were measured locally. Consequently, ASDAS-CRP, ASDAS-Q using the qCRP and ASDAS-ESR were calculated. The absolute agreement on the disease activity category ascertainment was analysed with cross-tabulations and weighted Cohen’s kappa. Bland–Altman plots and intraclass correlation coefficients (ICCs) were used to analyse the criterion validity. Results: Overall, 251 axial SpA patients were included in the analysis. The mean qCRP value (6.34 ± 11.13 mg/l) was higher than that of routine laboratory CRP (5.26 ± 9.35 mg/l). The ICC for routine laboratory CRP versus qCRP was 0.985 [95% confidence interval (CI): 0.972–0.991]. Comparing ASDAS-Q with ASDAS-CRP, 242 of 251 (96.4%) patients were assigned to the same disease activity categories with a weighted Cohen’s kappa of 0.966 (95% CI: 0.943–0.988) and ICC of 0.997 (95% CI: 0.994–0.999). Conclusions: ASDAS-Q showed an almost perfect agreement with ASDAS-CRP in the assignment to specific disease activity categories. Consequently, ASDAS-Q using the qCRP value can be applied as an accurate and quickly available alternative to ASDAS-CRP, thus facilitating the implementation of the treat-to-target concept in clinical trials and clinical routine.

Validation of the Simplified Disease Activity Index (SDAI) with a quick quantitative C-reactive protein assay (SDAI-Q) in patients with rheumatoid arthritis: a prospective multicenter cross-sectional study

“…The current research project was conducted as part of a joint, higher level, multicenter research project to validate different disease activity scores using a qCRP assay, including the validation of the ASDAS based on a qCRP assay. 23 …”

“…Exclusion criteria for study participation were a previously known clinically significant anemia, meaning a hemoglobin-concentration <10 g/dl (<6.2 mmol/l) or signs of an acute infection. 23 A structured rheumatologic assessment was performed in all study patients, including joint counts, patients’ global assessment of disease activity, evaluator’s global assessment of disease activity, and laboratory assessment. Patient’s and evaluator’s global assessments of disease activity were assessed on a visual analogue scale (VAS) from 0 cm = inactive to 10 cm = very active.…”

“…Instead of whole blood from the collection system, the qCRP measurement could also be performed with ethylenediaminetetraacetic acid (EDTA) or heparin whole blood, when the collection system was no more available or blood in the collection system was already coagulated. 23 …”

“…The intake of non-steroidal anti-inflammatory drugs (NSAIDs) was quantified by calculating the NSAID equivalent score (modified formula according to Dougados et al. 35 ) 23 …”

“…In the past, we have already validated the Ankylosing Spondylitis Disease Activity Score (ASDAS) using a qCRP assay (called ASDAS-Q) in a single-center pilot study 22 and in a multicenter study with a higher sample size. 23 This qCRP assay can be also used for SDAI calculation (as SDAI-Q). As a timely available composite index containing an acute-phase reactant, the SDAI-Q may combine the advantages of the conventional SDAI as well as the advantages of the CDAI, but has not been validated yet.…”