Background Calprotectin (S100A8/9, MRP8/14) is a promising circulating biomarker reflecting disease activity in patients with rheumatoid arthritis (RA). In two small previous studies in RA patients1,2, serum calprotectin correlated with ultrasound synovial inflammation.
Objectives To investigate associations between serum calprotectin, clinical and ultrasound-determined disease activity in a larger cohort of RA patients in a cross-sectional study.
Methods A total of 167 patients with RA (134 females) were enrolled in this study. All patients underwent clinical assessment (SJC, TJC, DAS28-ESR) and ultrasound examination according to the US-7 score3 to assess synovitis by gray-scale (GS) and power Doppler (PD) using semiquantitative grading (0-3). Serum calprotecin was measured by ELISA. Associations between serum calprotectin, C-reactive protein (CRP) and clinical as well as ultrasound findings were explored using Spearman's correlation coefficient. A multiple regression analysis was used to determine the predictive value of calprotectin (mg/l), CRP (mg/l) and DAS28 for GS and PD synovitis score.
Results Serum calprotectin significantly correlated with DAS28 (r=0.357, p<0.001), SJC (r=0.258, p=0.001), TJC (r=0.181, p<0.05), ESR (r=0.386, p<0.001) and particularly with CRP levels (r=0.540, p<0.001). In addition, calprotectin was also associated with GS (r=0.341, p<0.001) and PD synovitis (r=0.313, p<0.001).
Using a multivariate linear regression model with calprotectin, CRP and DAS28-FW as explanatory variables, calprotectin and DAS28, but not CRP, were significant predictors for GS (β=0.371, p<0.001; β=0.598, p<0.001, resp.) and PD synovitis (β=0.346, p<0.001; β=0.379, p<0.001, resp.).
Conclusions This study confirms in a large cohort of RA patients that serum levels of calprotectin are significantly associated with clinical, laboratory and ultrasound assessments of disease activity. Calprotectin is more closely associated with local joint inflammation than CRP and thus may represent a more specific circulating biomarker for monitoring synovial inflammation in RA patients.
Hammer HB, Fagerhol MK, Wien TN, Kvien TK. The soluble biomarker calprotectin (an S100 protein) is associated to ultrasonographic synovitis scores and is sensitive to change in patients with rheumatoid arthritis treated with adalimumab. Arthritis Res Ther. 2011;13(5):R178.
Hurnakova J, Hanova P, Hulejova H, et al. Serum calprotectin (S100A8/9) correlates with clinical and ultrasound outcomes in patients with early rheumatoid arthritis. In Ann Rheum Dis. 2014; Suppl (2):658–658.
Backhaus M, Ohrndorf S, Kellner H, Strunk J, Backhaus TM, Hartung W, et al. Evaluation of a novel 7-joint ultrasound score in daily rheumatologic practice: a pilot project. Arthritis Rheum. 2009 Sep 15; 61(9):1194-1201.
Acknowledgements This work was supported by the project (Ministry of Health, Czech Republic) for consensual development of research organization 023728, IGA grant No. NT12437 and GAUK grant No. 1010213.
Disclosure of Interest None declared