Association of circulating levels of anti-CarP antibodies with disease activity, disability and radiological damage in rheumatoid arthritis patients: an open-label, observational study

Autoantibodies directed against carbamylated proteins (anti-CarP) have been recently identified as predictors for RA development. The aim of this study was to determine the positivity of anti-CarP antibodies in a real-life cohort of RA patients and their association with radiological damage, disability and disease activity. In this open-label, observational, cross-sectional study 69 RA patients and 16 healthy controls (HC) were recruited. The study was approved by institutional Ethical Committee. Circulating levels of anti-CarP antibodies were determined by commercial ELISA anti-CarP quantitative sandwich immunoassay. Articular X-rays were evaluated to define the presence of bone erosions. Disease activity (DAS28-CRP) and disability (HAQ-DI) were assessed. Pearson χ² test, Wilcoxon test or Kruskall-Wallis test was used. Spearman rank-order correlation coefficient was applied for continuous variables. Multivariable logistic regression model was performed. Anti-CarP positivity was found in 35% of RA patients and in no HC. One quarter of seronegative RA patients were anti-CarP positive. A positive correlation between levels of anti-CarP antibodies with DAS28-CRP (p = 0.0003; Spearman r = 0.4829) and HAQ-DI (p = 0.0003; Spearman r = 0.4253) was found. 87% of anti-CarP positive patients had erosions. At multivariable logistic regression analysis, RA disease activity (OR 1.31, 95% CI [1.14, 1.63]) and circulating levels of anti-CarP antibodies (OR 1.66, 95% CI [1.28, 2.37]) were independent predictors of bone erosions. Our study confirms that anti-CarP antibodies are associated with a more aggressive RA course and are independent predictors of bone erosions.