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

Abstract

Objectives: The Simplified Disease Activity Index (SDAI) is a recommended composite score for assessing the remission status in patients with rheumatoid arthritis (RA). However, determination of C-reactive protein (CRP) levels takes several hours and sometimes days and limits the use of the SDAI in the clinical setting. The aim of this study was to validate the SDAI using a quick quantitative C-reactive protein (qCRP) assay (as SDAI-Q) in RA patients. Design: This is a multicenter, prospective, cross-sectional pilot study in RA patients. Methods: Adult patients (⩾18 years) with a clinical diagnosis of RA were recruited between January 2020 and September 2020 from five rheumatologic centers located in Berlin, Germany. SDAI, SDAI-Q, Clinical Disease Activity Index (CDAI), and DAS28 scores comprising CRP, qCRP, or erythrocyte sedimentation rate (ESR) were calculated. The agreement of disease activity categories was analyzed using cross tabulations and weighted Cohen’s kappa. The agreement of numerical values was analyzed with Bland–Altman plots and intraclass correlation coefficients (ICCs). Results: Overall, 100 RA patients were included in the statistical analysis. The mean value of qCRP (7.89 ± 16.98 mg/l) was slightly higher than that of routine laboratory CRP (6.97 ± 15.02 mg/l). Comparing SDAI and SDAI-Q, all patients were assigned to identical disease activity categories. Agreement of disease activity categories by CDAI and SDAI/SDAI-Q was observed in 93% with a weighted Cohen’s kappa of 0.929 (95% confidence interval (CI) = 0.878; 0.981). Conclusion: The SDAI-Q showed an absolute agreement regarding the assignment of disease activity categories in comparison with the conventional SDAI. Therefore, the SDAI-Q may facilitate the application of a treat-to-target concept in clinical trials and clinical routine as a quickly available disease activity score incorporating CRP as an objective parameter.

Evaluation of the Disease Activity index for PSoriatic Arthritis (DAPSA) with a quick quantitative C reactive protein assay (Q-DAPSA) in patients with psoriatic arthritis: a prospective multicentre cross-sectional study

“…This multicentre, cross-sectional pilot study was performed as part of a larger, overaching study project to evaluate the performance of different rheumatologic disease activity scores based on a qCRP assay, including a qCRP-based ASDAS 17 and a qCRP-based SDAI. 18 …”

“…19 20 The qCRP measurement was implemented as described in the assay instructions 19 and takes approximately 2 min. 18 All qCRP values were displayed in mg/L with one decimal place by the measuring instrument. 19 Quality controls using the ‘QuikRead go wrCRP Control’ (Aidian Oy) solution were conducted one time per week.…”

“…Similar to our other study, 18 this is a pilot study for the evaluation of the Q-DAPSA, and, thus, we set a sample size of 100 patients with PsA.…”

“…This multicentre, cross-sectional pilot study was performed as part of a larger, overaching study project to evaluate the performance of different rheumatologic disease activity scores based on a qCRP assay, including a qCRP-based ASDAS 17 and a qCRP-based SDAI. 18 Participants were recruited between January 2020 to October 2020 from five different rheumatologic centres located in Berlin, Germany, including three rheumatologic outpatient practices and two specialised academic university hospitals. Patients were eligible for study participation if they were ≥18 years of age, had a clinical diagnosis of PsA and had given written informed consent.…”

“…In other studies, we could already validate a qCRP-based Ankylosing Spondylitis Disease Activity Score (ASDAS-Q) in patients with axial SpA 16 17 and a qCRP-based Simplified Disease Activity Index (SDAI-Q) in patients with rheumatoid arthritis (RA). 18 In the current study, we aimed to evaluate a DAPSA using a quick quantitative CRP assay (so called Q-DAPSA). The Q-DAPSA could be beneficial for the disease activity assessment in patients with PsA due to fast clinical availability while still including the CRP as objective disease activity parameter.…”