Measurement of plasma calprotectin as an indicator of arthritis and disease activity in patients with inflammatory rheumatic diseases.

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.