ORIGINAL ARTICLE Accuracy of CD64 expression on neutrophils and monocytes in bacterial infection diagnosis at pediatric intensive care admission Alberto García-Salido 1 & A. Martínez de Azagra-Garde 1 & M. A. García-Teresa 1 & G. De Lama Caro-Patón 1 & M. Iglesias-Bouzas 1 & M. Nieto-Moro 1 & I. Leoz-Gordillo 1 & C. Niño-Taravilla 1 & M. Sierra-Colomina 1 & G. J. Melen 2 & M. Ramírez-Orellana 2 & A. Serrano-González 1 Received: 20 December 2018 / Accepted: 23 January 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract The CD64 receptor has been described as an interesting bacterial infection biomarker. Its expression has not been studied in previously healthy children admitted to pediatric critical care unit (PICU). Our objective was firstly to describe the CD64 expression and secondly study its diagnostic accuracy to discriminate bacterial versus viral infection in this children. We made a prospective double-blind observational study (March 2016–February 2018). A flow cytometry (FC) was done from peripheral blood at PICU admission. We studied the percentage of CD64+ neutrophils and the CD64 mean fluorescence intensity (MFI) on neutrophils (nCD64) and monocytes (mCD64). Statistical analyses were performed with non-parametric tests (p < 0.05). Twenty children in the bacterial infection group (BIG) and 25 in the viral infection group (VIG). Children in BIG showed higher values of CD64+ neutrophils (p = 0.000), nCD64 (p = 0.001), and mCD64 (p = 0.003). In addition, CD64+ neutrophils and nCD64 expression have positive correlation with procalcitonin and C reactive protein. The nCD64 area under the curve (AUC) was 0.83 (p = 0.000). The %CD64+ neutrophils showed an AUC of 0.828 (p = 0.000). The mCD64 AUC was 0.83 (p = 0.003). The nCD64 and %CD64+ neutrophils also showed higher combined values of sensitivity (74%) and specificity (90%) than all classical biomarkers.In our series CD64 expression allows to discriminate between bacterial and viral infection at PICU admis- sion. Future studies should confirm this and be focused in the study of CD64 correlation with clinical data and its utility as an evolution biomarker in critical care children. Keywords Viral infection . Bacterial infection . Critical care . Flow cytometry . CD64 . Sensitivity . Specificity Introduction Infectious diseases are a main cause of admission in pediatric intensive care unit (PICU). Bacterial and viral infections are the principal causes in healthy children. Added to the support- ive therapies used in PICU, to start a correct and prompt an- timicrobial treatment is critical in order to anticipate complications and minimize morbidity [1]. The inexistence of accurate and precocious biomarkers of viral or bacterial infection forces the physician to initiate broad spectrum ther- apies that maybe are not indicated [8]. This, plus a not ade- quate de-escalation antibiotherapy politic, increases the prob- ability of bacterial antibiotic resistance. Also, the PICU and hospital stance are prolonged with an impact in cost each admission [8, 13, 23]. Nowadays, in acute or critical context, early etiological recognition of infection remains a matter of concern. There is no doubt about how the etiological diagnosis of infection has been improved in recent years. The introduction of mo- lecular diagnosis tools, such reactive polymerase chain reac- tion or rapid immunological test, has collaborated in this new status. But, gold standard, as the blood culture or other body fluid cultures, requires at least 24–48 h to offer its results. Also, negative cultures do not completely exclude the pres- ence of suspected bacterial infection [8, 13]. Biomarkers that may facilitate early diagnosis and the assessment of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10096-019-03497-z) contains supplementary material, which is available to authorized users. * Alberto García-Salido citopensis@yahoo.es 1 Pediatric Critical Care Unit, Hospital Infantil Universitario Niño Jesús, Avenida Menéndez Pelayo, 65 Madrid, Spain 2 Department of Pediatric Hematology and Oncology, Hospital Infantil Universitario Niño Jesús, Madrid, Spain European Journal of Clinical Microbiology & Infectious Diseases https://doi.org/10.1007/s10096-019-03497-z