Comparison of Fc gamma receptor expression on neutrophils with procalcitonin for the diagnosis of sepsis in critically ill patients

Background and objective: The expression of Fc receptors for IgG (Fc gamma Rs) on neutrophils, including CD16, CD32 and CD64, may be modulated in response to sepsis. We investigated the expression of Fc gamma Rs on neutrophils and procalcitonin (PCT) as biomarkers of sepsis among critically ill patients. Methods: This prospective study was conducted in a 24-bed respiratory intensive care unit between July 2007 and June 2008. Critically ill patients requiring mechanical ventilation were enrolled and categorized into three groups: those with systemic inflammatory response syndrome (SIRS), those with severe sepsis and those with septic shock. Expression of Fc gamma Rs on neutrophils was quantitatively measured by flow cytometry immediately after enrolment of the patient. Serum PCT levels were also measured. Receiver operating characteristic (ROC) curves were used to evaluate the performance of Fc gamma R expression and PCT as biomarkers of sepsis. Results: Sixty-six patients were enrolled, including 11 with SIRS, 31 with severe sepsis and 24 with septic shock. Nineteen healthy volunteers served as normal controls. CD64 was upregulated, CD16 was downregulated and CD32 remained unchanged during sepsis. CD64 expression and the ratio of CD64/CD16 increased significantly with the severity of sepsis. However, serum PCT levels were not significantly different between SIRS and severe sepsis patients. CD64, CD64/CD16 and PCT all significantly predicted sepsis, septic shock and bacteraemia. As assessed using ROC curves, CD64 was better than PCT for differentiating SIRS from severe sepsis and septic shock. CD64 and CD64/CD16 were associated with mortality. Conclusions: CD64 and CD16 were differentially modulated by sepsis. CD64, CD64/CD16 and PCT may be biomarkers of sepsis. CD64 was better than PCT for identifying patients who required treatment with antibiotics.