Calprotectin as an early biomarker of bacterial infections in critically ill patients: an exploratory cohort assessment.

BACKGROUND Calprotectin is the most abundant protein in the cytosolic fraction of neutrophils, and neutrophil degranulation is a major response to bacterial infections. OBJECTIVES To assess the value of plasma calprotectin as an early marker of bacterial infections in critically ill patients and compare it with the corresponding values for procalcitonin (PCT), C-reactive protein (CRP) and white blood cell count (WBC). METHODS We measured daily plasma calprotectin levels in 110 intensive care unit patients using a newly developed turbidimetric assay run on clinical chemistry analysers. The likelihood of infection was determined according to the International Sepsis Forum criteria. RESULTS Overall, 58 patients (52.7%) developed a suspected or confirmed bacterial infection. Plasma calprotectin predicted such infections within 24 hours with an area under the receiver operating characteristics curve (ROC area) of 0.78 (95% CI, 0.68-0.89). The ROC area for calprotectin was significantly greater than the corresponding ROC areas for WBC (P < 0.001) and PCT (P = 0.02) but only marginally better than the ROC area for CRP (0.71; 95% CI, 0.68-0.89). CONCLUSION Plasma calprotectin appears to be a useful early marker of bacterial infections in critically ill patients, with better predictive characteristics than WBC and PCT.