October 26, 2018
McClosky ME, Cimino Brown D, Weinstein NM, et al. Prevalence of naturally occurring non-AB blood type incompatibilities in cats and influence of crossmatch on transfusion outcomes. J Vet Intern Med. 2018 Oct 11. doi: 10.1111/jvim.15334
When it comes to people, we understand the importance of knowing and understanding blood types in regards to transfusions. It is also clinically important to know that cats have an AB blood group system with naturally occurring anti-A and anti-B alloantibodies. Through research and practice, it is shown worldwide that all type B cats (after 6-8 weeks of age) have anti-A antibodies with high-titered hemaagglutinins and hemolysins. On the opposite side, type A cats have relatively weak anti-B antibodies with decreased hemaagglutinin and hemolysin titers generally. The percentage of type A cats with detectable anti-B antibodies is highly variable.
Clinically, the presence of strong anti-A alloantibodies has led to reports of severe, acute hemolytic transfusion reactions characterized by hypotension, bradycardia, apnea, urination, defecation, vomiting, hemoglobinemia, and hemoglobinuria occurring in type B cats receiving type A blood. Anti-B antibodies produce a milder reaction such as slight hemoglobinemia, hemoglobinuria and bilirubinuria in type A cats receiving type B blood, or often such type mismatched transfusions are associated with a shortened life-span of the transfused red blood cells, with a mean half-life of 2 days. Accordingly, universal agreement is that all cat blood donors and recipients should be blood typed – for A, B, or AB antigens – before a red blood cell (RBC) transfusion. There are point-of-care feline blood typing kits available for determination of type within the AB blood group system for use in clinical practice.
A new feline RBC antigen, Mik, was recognized in 2007 (Winn Feline Foundation provided instrumental funding for this research). This discovery occurred when a type A-matched RBC transfusion resulted in an acute hemolytic transfusion reaction in a Mik-negative cat with anti-Mik alloantibodies that received blood from a Mik-positive donor. Anti-Mik antibodies are naturally occurring but a RBC transfusion could lead to this development in a Mik-negative cat. It appears that Mik is a common RBC antigen (few Mik-negative cats have been identified); yet, typing for the Mik antigen is limited due to a lack of typing reagent. While the standard recommendation has been to crossmatch for cats that receive blood > 4 days after their first transfusion, due to the naturally occurring anti-Mik alloantibodies and the possibility of other non-AB, non-Mik alloantibodies in cats prompts the consideration for a crossmatch before their first transfusion in cats.
The authors’ primary goal of this retrospective study was to determine the prevalence of naturally occurring, non-AB blood type incompatibilities in cats having a crossmatch done in anticipation of a blood transfusion or renal transplantation. Another goal was to compare transfusion outcomes in cats with and without a pretransfusion crossmatch.
The results of the study documented major crossmatch incompatibilities in 23 of 154 transfusion-naïve cats (14.9%) and in 15 of 55 previously transfused cats (27%). Blood type specific packed RBCs (pRBCs) were given to 167 and 82 cats with and without a crossmatch, respectively. Transfusion reactions involving fever occurred more often in cats that were not crossmatched (10.1%) prior to transfusion compared to crossmatched (2.5%) pRBCs. A large percentage (76%) of cats receiving pRBC survived to hospital discharge. Performing a crossmatch was not associated with improved survival to discharge or at 30 or 60 days posttransfusion.
As a conclusion, the authors state the prevalence of naturally occurring non-AB incompatibilities is sufficiently elevated to justify a recommendation to perform a crossmatch before all (including the first) RBC transfusions in cat. (VT)