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

Background Objective 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. 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 Methods Three hundred cats that received an RBC transfusion, with or without a major crossmatch performed. Retrospective study. Results Conclusions and Clinical Importance 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. 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.