Simultaneous quantitative analysis of FcγRI (CD64) expression on neutrophils and monocytes: A new, improved way to detect infections

We performed simultaneous quantitative flow cytometric analysis of neutrophil and monocyte FcγRI (CD64) in 289 hospitalized febrile patients. Microbiological evaluation or clinical diagnosis confirmed bacterial (n = 89) or viral (n = 46) infection in 135 patients. Patient data were compared with data from 60 healthy controls.The average number of FcγRI on the surfaces of both neutrophils and monocytes was significantly increased in patients with febrile viral and bacterial infections, compared to healthy controls. Furthermore, we describe a novel marker of febrile infection, designated ‘CD64 score point’, which incorporates the quantitative analysis of FcγRI expressed on both neutrophils and monocytes, with 94% sensitivity and 98% specificity in distinguishing between febrile infections and healthy controls. By contrast, analysis of FcγRI expression on neutrophils and monocytes displayed poor sensitivity (73% and 52%) and specificity (65% and 52%) in distinguishing between bacterial and viral infections, and the levels did not differ significantly between systemic (sepsis), local, and clinically diagnosed bacterial infections.In summary, our results clearly show that the increased number of FcγRI on neutrophils and monocytes is a useful marker of febrile infection, but cannot be applied for differential diagnosis between bacterial and viral infections or between systemic and local bacterial infections.