Neutrophil CD64 as a marker of infection in patients admitted to the emergency department with acute respiratory failure.

Introduction: Cluster of differentiation 64 (CD64) is expressed on neutrophils during bacterial infections and sepsis. The aim of our study was to assess the CD64 expression in patients admitted to the emergency department (ED) with a triage diagnosis of acute respiratory failure (ARF) and/or dyspnea and to verify a relationship between its value and the presence of infection.

Methods: We assessed neutrophil CD64 expression in peripheral blood of patients admitted to the ED with a diagnosis of ARF and/or dyspnea from September 2012 to April 2013. We measured CD64 index by flow cytometry (Leuko64™ kit) and classified patients as infected within 12 hours from admission, without an infection within 12 hours but infected within 72 hours from admission, and not infected. The primary outcome was differentiating CD64 values of patients with a diagnosis of infection within 12 hours and 72 hours from admission, from those of patients without a diagnosis of infection. The secondary outcome was verifying a relationship between CD64 values and patients' characteristics, Sequential Organ Failure Assessment score, and intensive care unit admission.

Results: Of 212 patients included in the study, 40.1% were classified as infected within 12 hours from admission, 20.3% were without an infection 12 hours after admission but were infected within 72 hours, and 39.6% were not infected. The median CD64 index was higher in patients with an infection on admission (CD64 index: 3.58) than in those not considered infected (CD64 index: 1.37), P<0.0001. Among patients not infected at admission, the CD64 index was higher in those with an infection detected during the following hours of observation (CD64 index: 2.75) than in patients without a diagnosis of infection (CD64 index: 1.28), P<0.0001. A CD64 index >3.65 showed a sensitivity of 94.6%, a specificity of 86.8%, and an area under the receiver-operating characteristic curve of 0.952 for prediction of intensive care unit admission.

Conclusion: CD64 index could represent a useful diagnostic tool for differential diagnosis of ARF in the ED.