Neutrophil CD64 Expression as a Diagnostic Marker of Bacterial Infection in Febrile Children Presenting to a Hospital Emergency Department

Background: The expression of CD64 (Fc gamma receptor) is increased in neutrophils from an almost negligible value to a marked level in patients with bacterial infections. CD64 expression on neutrophils might therefore be useful to differentiate between bacterial and viral infections in young children. We evaluated the usefulness of CD64 as a marker for the diagnosis of bacterial infections in children up to the age of 3 years and its ability to differentiate between bacterial and viral infections. Methods: Blood samples were drawn from 70 children aged 3 years or younger who presented to the pediatric emergency department with fever as their main complaint. Thirty-eight children were diagnosed as having bacterial infection and 32 as having viral infection. The control group included 39 healthy children. CD64, C-reactive protein (CRP), and procalcitonin levels were determined for each child. The sensitivity and specificity of these parameters were calculated. Results: Neutrophil expression of CD64 was significantly higher in the bacterial infection group compared with the viral infection and the control groups (P < 0.0001). Raising the cutoff for diagnosis of bacterial disease lowered the sensitivity but improved the specificity. CD64 was found to have a very high sensitivity (94.7%), but its specificity was poor (46.5%). No significant differences were found between the diagnostic performance of CD64 and that of CRP: both have high sensitivity and low specificity (94.7% and 47.9%, respectively, for CRP). In contrast, procalcitonin had a better specificity (91%), but its sensitivity reached only 71.9%. CD64 expression was increased in patients with respiratory syncytial virus-related infections compared with that in patients with other viral infections and was similar to that found during bacterial illness. Conclusions: Neutrophil CD64 expression is a sensitive marker for diagnosing bacterial infection in young children, but as it is also raised in viral infection, it lacks specificity.