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.