Background/Purpose:  Calprotectin (MRP8/MRP14, S100A8/A9) is a major leukocyte protein previously shown to be associated with disease activity in patients with established rheumatoid arthritis (RA). Some studies indicate that it may be a more accurate measure of joint inflammation than erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). Our objective was to compare the associations of calprotectin, ESR and CRP with clinical and ultrasound (US) measures of inflammation in patients with early RA, both before and after 12 months of aggressive disease-modifying antirheumatic drug (DMARD) treatment.

Methods:  RA-patients (n=238) who fulfilled the 2010 ACR/EULAR classification criteria were recruited to the ARCTIC trial between 2010 and 2013. All patients had symptom duration from first swollen joint <2 years and were DMARD-naïve with indication for DMARD treatment. Calprotectin in EDTA-plasma was analyzed by ELISA in 212 patients at baseline and 163 patients at 12 months. US inflammation was evaluated using a standardized protocol with semi-quantitative scoring 0-3 for grey-scale (GS) and power Doppler (PD) in 32 joints (1). Clinical inflammation was assessed by 44 swollen joint count (SJC44), Ritchie Articular Index (RAI), ESR and CRP. Disease activity score (DAS) was calculated. Cross-sectional relationships were assessed by Spearman’s correlations.

Results:  A total of 212 patients were included: 61% female, 71% RF positive, 83% ACPA positive, mean (SD) age 50.8 (13.8) years, mean DAS 3.4 (1.2), median [25, 75 percentile] disease duration 5.9 [2.9, 10.6] months. At 12 months mean DAS was 1.2 (0.7); 75.5% were in remission according to DAS, 15.3% low, 8.7% moderate and 0.5% high DAS. The median baseline/12 month calprotectin was 1020 [562, 2153]/478[293, 794] μg/L, ESR 19 [11, 30]/9[5, 15] mm/h and CRP 7 [3, 17]/3[1, 5] mg/L. Calprotectin was significantly correlated with clinical and US markers of inflammation before treatment onset (table, figure A). After 12 months of treatment, calprotectin had a weaker, but statistically significant correlation with US scores, while no significant associations between ESR/CRP and US scores were found (figure B).  

Conclusion:   Calprotectin was correlated with inflammation assessed by ultrasound before onset of DMARD treatment, and the association was also present after 12 months of DMARD treatment. This association was not found for ESR and CRP. The data support that calprotectin might be of interest when assessing disease activity in different stages of RA. References: 1) Hammer HB et al Ann Rheum Dis 2011

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/calprotectin-levels-correlate-with-inflammation-in-early-rheumatoid-arthritis-before-disease-modifying-antirheumatic-drug-treatment-and-after-12-months-of-treatment/