Objective

To investigate if the plasma level of the granulocyte protein calprotectin is a useful indicator of severity of arthritis in patients with inflammatory rheumatic diseases, and to analyze which factors contribute to the raised plasma calprotectin levels.

Methods

Plasma calprotectin levels were measured by ELISA: In a cross sectional study of 154 patients with various inflammatory rheumatic diseases, calprotectin levels were correlated with laboratory and clinical variables.

Results

The plasma levels of calprotectin and C-reactive protein (CRP) correlated significantly with the clinical evaluation of swollen joints (r= 0.51, p< or= 0.01 and r= 0.29, p< or= 0.01, respectively). Calprotectin levels, but not CRP levels or erythrocyte sedimentation rate, were significantly lower in patients with no swollen joints than in patients with one or more swollen joints (2613.6 micrograms/l vs 6287.0 micrograms/l, p< 0.001). A significant correlation between calprotectin and number of neutrophils was demonstrated (r= 0.43, p< or= 0.01), indicating that circulating neutrophils contribute to plasma calprotectin levels.

Conclusion

The plasma calprotectin level may be a useful indicator of arthritis in inflammatory rheumatic diseases.