IntroductionHemolysis 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.MethodsDonor- 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. Assoc