Prevalence of naturally occurring non‐AB blood type incompatibilities in cats and influence of crossmatch on transfusion outcomes

BACKGROUND: Recognition of the feline red blood cell (RBC) antigen Mik and the presence of naturally occurring anti‐Mik antibodies resulting in acute hemolytic transfusion reactions prompted the recommendation to perform a crossmatch before a cat's first RBC transfusion, but this guideline has not yet become a standard practice. OBJECTIVE: To determine the prevalence of naturally occurring non‐AB alloantibodies detectable by tube crossmatch, and to compare transfusion outcomes in cats with and without a crossmatch performed. ANIMALS: Three hundred cats that received an RBC transfusion, with or without a major crossmatch performed. METHODS: Retrospective study. RESULTS: Major crossmatch incompatibilities were documented in 23 of 154 transfusion‐naive cats (14.9%) and in 15 of 55 previously transfused cats (27%; P = 0.042). Type‐specific packed RBCs (pRBCs) were administered to 167 and 82 cats with and without a crossmatch, respectively. Median volume of pRBCs administered during the first transfusion was 5.3 mL/kg (range, 2.4‐18 mL/kg). Median change in PCV scaled to dose of pRBCs was +0.8%/mL/kg; administration of crossmatch‐compatible pRBCs was not associated with a greater increase in PCV. Febrile transfusion reactions occurred more often in cats that received non‐crossmatched (10.1%) compared to crossmatched (2.5%) pRBCs (P = 0.022). Seventy‐six percent of cats that received pRBC transfusions survived to hospital discharge. A crossmatch was not associated with improved survival to discharge or at 30 or 60 days posttransfusion. CONCLUSIONS AND CLINICAL IMPORTANCE: The prevalence of naturally occurring non‐AB incompatibilities is sufficiently high to justify the recommendation to perform a crossmatch before all (including the first) RBC transfusions in cats.