Serum Calprotectin As a Marker for Disease Activity and Severity in Adult-onset Still's Disease

Objective: Calprotectin is a calcium-binding cytosolic protein of the neutrophil, monocyte, and macrophage, and its secretion increases during activation of these cells. Our objective was to measure serum calprotectin concentrations in patients with adult-onset Still's disease (AOSD) and to correlate serum calprotectin with the activity and severity of AOSD.

Methods: We enrolled 25 patients with AOSD and 30 age- and sex-matched healthy controls. Thirty-one serum samples were obtained from patients with AOSD during active or inactive disease and were assayed for calprotectin by ELISA. Clinical and laboratory data related to disease activity and severity were collected at the same time, and systemic scores for disease severity were calculated.

Results: Mean calprotectin levels in patients with AOSD were significantly higher than in controls (57.11 +/- 25.38 ng/ml vs 34.90 +/- 4.85 ng/ml, respectively; p < 0.05). Patients with active AOSD had a significantly higher mean calprotectin level than those with inactive disease (61.26 +/- 25.59 ng/ml vs 35.32 +/- 5.90 ng/ml; p < 0.05). Calprotectin levels decreased significantly after treatment in all 6 patients with AOSD from whom followup samples were obtained (p = 0.028). Serum calprotectin showed strong correlations with serum ferritin (r = 0.686, p < 0.001), lactate dehydrogenase (r = 0.647, p < 0.001), leukocyte count (r = 0.774, p < 0.001), aspartate aminotransferase (r = 0.387, p = 0.042), and C-reactive protein (r = 0.588, p = 0.001), but not with erythrocyte sedimentation rate, arginine aminotransferase, hemoglobin, or platelet count. Serum calprotectin showed a significant correlation with AOSD systemic scores, reflecting disease severity (r = 0.803, p < 0.001).

Conclusion: Serum calprotectin increased in patients with AOSD, in close correlation with disease activity and severity. These findings suggest that serum calprotectin can provide a reliable clinical marker for monitoring the disease activity and severity of AOSD.