Comparing Absolute Neutrophil Counts of Children With Sickle Cell Disease With and Without the Duffy Null Phenotype.

While nonpathogenic, the Duffy null phenotype (DN) lowers circulating neutrophils. DN is common among youth with sickle cell disease (SCD), but its implications on absolute neutrophil counts (ANC) and hydroxyurea over time are unclear. Our retrospective review found that all children who were not receiving hydroxyurea had stable ANC through age 9 years, but those with DN had lower mean ANC starting at 6 years of age. Among hydroxyurea users, ANC increased over time, regardless of DN status, suggesting opportunities to optimize hydroxyurea. Future studies of hospitalized and older individuals are needed to further examine DN's impact on people with SCD.