Clinical significance of serum calprotectin level for the disease activity in active rheumatoid arthritis with normal C-reactive protein.

Background: There was limited data concerning predicting ability of calprotectin for disease activity of rheumatoid arthritis (RA) patients with normal C-reactive protein (CRP) level. This study was conducted to evaluate serum calprotectin levels in active RA patients and analyze its predicting value for disease activity evaluation despite normal CRP level.

Methods: A total of 162 patients with active RA patients with normal CRP levels and 57 healthy subjects were enrolled. Serum calprotectin was measured by using a commercially available enzyme-linked immunosorbent assay (ELISA), and baseline clinical characteristics were collected. The DAS-28 scores were evaluated as indictors of disease activity. The predicting value of calprotectin in disease activity of RA patients with normal CPR was analyzed by using univariate and multivariate analysis and receiver operating characteristic curve.

Results: Serum levels of calprotectin of patients with active RA were significantly higher than that of the healthy controls (3.5±3.2 vs. 2.5±0.8, P<0.01). Univariate analysis showed that serum calprotectin levels were significantly associated with the disease activity of RA. The mean serum calprotectin levels of patients with a high disease activity (DAS-28>5.1) was significantly higher than that of RA patients with low-moderate disease activity (4.3±3.5 vs. 2.6±1.1, P<0.01). Serum calprotectin levels also was evaluated as an independent predictive factor for disease activity of RA in multivariate analysis (OR, 2.31; 95% CI, 1.12-6.84; P<0.01).

Conclusions: Serum calprotectin levels can be used as a promising indictor for disease activity in active RA patients while CRP fails to do so.