Hematocrit of granulocyte concentrates regulates neutrophils' function and viability

BACKGROUND: Granulocyte transfusion is a supportive therapy for neutropenic patients with refractory infections. Granulocyte concentrates (GCs) derived from apheresis or whole blood donations exhibit variable hematocrit levels (0.09 L/L vs. 0.24 L/L), which may influence neutrophil viability and antimicrobial functions during storage. This study investigates the impact of hematocrit on neutrophil viability and antimicrobial functions during storage. STUDY DESIGN AND METHODS: Two ABO-compatible whole blood donations were pooled, split, and processed using the Reveos automated system to obtain two residual leukocyte products (RLPs). Each RLPs was further manipulated to generate four hematocrit conditions (0.5 L/L, 0.24 L/L, 0.09 L/L or 0 L/L) by controlled RBC enrichment or depletion. Neutrophil viability, activation markers, chemotaxis, phagocytosis, and reactive oxygen species (ROS) production were assessed at baseline and after 24 h of storage. Cytokine profiles and biochemical parameters were also analyzed. RESULTS: After 24 h, neutrophil viability dropped to 51% in low hematocrit conditions (0.00 and 0.09 L/L) but remained above 90% at 0.24 and 0.50 L/L. Low hematocrit RLPs exhibited increased activation (CD66b↑, CD62L↓), impaired chemotaxis (-33%), phagocytosis (-40%), and ROS production (-80%), along with elevated proinflammatory cytokines (IL-1α, IL-1β, TNF-α). In contrast, intermediate hematocrit (0.24 L/L) preserved neutrophil integrity and function, while further enrichment (0.50 L/L) provided no additional benefit. DISCUSSION: These findings suggest that hematocrit may be an important determinant of RLP quality and, by extension, GC performance. An intermediate level (0.24 L/L) optimally maintains neutrophil viability and antimicrobial functions during storage.