Donor- and unit-specific factors influencing hemolysis in stored canine and feline packed red blood cells

Introduction: Hemolysis during storage compromises the quality of canine and feline packed red blood cell (pRBC) units by shortening unit shelf-life, reducing oxygen-carrying capacity, increasing the risk of non-immune-mediated hemolytic transfusion reactions, and necessitating the discard of units when stock is limited. Methods: Donor- and unit-level determinants of percent hemolysis were investigated in a multicenter quality-control dataset comprising 5,583 canine and 3,176 feline pRBC units. Associations were assessed by univariable screening followed by multivariable statistical analysis. Results: In both species, multivariable analysis indicated higher percent hemolysis with longer storage duration, older donor age, and lower unit packed cell volume (PCV). Beyond these common patterns, dogs exhibited higher percentage hemolysis in DEA 1 positive units and larger unit volume was associated with lower percentage hemolysis. Overall, 28.3% of canine units and 6.5% of feline units exceeded 0.8% hemolysis, whereas 16.5 and 4.0%, respectively, exceeded 1%. Threshold exceedance increased markedly from 22-28 days of storage onward. Discussion: Based on one of the largest multicenter veterinary datasets to date, these findings reaffirm that storage hemolysis increases with storage duration and is further shaped by donor- and unit-level characteristics. These results may support more precise donor selection and unit release policies and reinforce hemolysis testing of units stored for ≥28 days.