Is the Use of Complete Blood Counts with Manual Differentials an Antiquated Method of Determining Neutrophil Composition in Newborns?

BACKGROUND: Automated complete blood counts (CBCs) provide imprecise measures of neonatal neutrophil composition due to the presence of nucleated red cells, which masquerade as white cells. Manual differentials (MDs) must be performed but can be flawed due to technician inexperience or limited cell counts. Our study evaluated whether flow cytometry could more accurately determine neutrophil composition in term newborns compared with adult controls. METHODS: Neutrophils were obtained by venipuncture in adults (n=10) and via cord blood from neonates delivered vaginally (n=21) or by primary cesarean section (n=17). Samples were processed by both flow cytometry and CBC with MD and results compared. Flow cytometry findings were verified using gene expression analysis of granule proteins. RESULTS: Immature-to-total neutrophil ratios were used to signify neutrophil composition. Flow cytometry was superior to manual differentials due to its ability to identify the earliest neutrophil forms. Significant differences between newborns and adults were determined using flow cytometry (0.12 versus 0.05; p=0.01), but not MDs (p=0.18). Neonates had similar findings irrespective of labor and method used. Verification of neutrophil maturity was completed using gene expression analysis of granule proteins. CONCLUSIONS: These results raise concerns about the accuracy of using CBCs with MDs to determine neutrophil composition. Further investigation of flow cytometry in clinical practice is warranted.