Blood Cell Counts and the Duffy Null Phenotype: Beyond Neutropenia.

The absence of Duffy antigen expression on red blood cells, caused by a single nucleotide polymorphism in the DARC/ACKR1 gene, confers protection against malaria and is associated with lower absolute neutrophil counts (ANC) in some studied populations. This study aimed to establish reference intervals for ANC and evaluate other hematologic parameters influenced by Duffy status in Brazilian individuals. In this prospective study, complete blood counts and Duffy phenotyping were performed in 311 healthy adult blood donors from two independent blood banks. Among participants, 51.4% were male, with a median age of 37 years, and 46.6% self-identified as Black or mixed-race. The Duffy null phenotype was observed in 146 individuals (46.9%), with lower male representation and higher prevalence among Black individuals. Duffy null individuals showed lower median white blood cell counts (5350 vs. 7060/μL) and ANC (median 2250 vs. 4070/μL), with a 95% reference range of 1180-4800/μL versus 2200-7250/μL. They also had a lower neutrophil percentage and higher relative counts of other leukocytes, without differences in absolute lymphocytes and eosinophils. Additionally, they exhibited higher erythrocyte counts, hemoglobin, hematocrit, platelet counts, and mean platelet volume. These findings support Duffy-specific reference intervals to avoid misclassification in diverse populations like Brazil.