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Feline Blood Group Compatibility

Clinician's Brief (Capsule)

Clinical Pathology

|December 2014

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Cats have one major blood group system: the AB blood group. Blood groups are determined by the presence of antigenic markers on the surface of RBCs; cats are either blood type A, B, or AB. Transfusion reactions stem from from naturally occurring alloantibodies in the recipient’s blood against a blood-type antigen in donor blood. Correct identification of feline blood types is necessary to prevent potentially fatal transfusion reactions. Type B cats receiving type A or AB blood can have a potentially fatal hemolytic transfusion reaction as type B cats have high anti-A alloantibody titers. Type A cats have low titers of anti-B alloantibodies, but can still experience premature destruction of RBCs if they receive type B or AB blood.

Transfusion reactions stem from from naturally occurring alloantibodies in the recipient’s blood against a blood-type antigen in donor blood.

This prospective study’s purpose was to assess if phenotyping using standard microplate agglutination produced the same results as genotyping (AA, Ab, or bb) when analyzing feline whole blood samples. Of the 112 cats used in this study, presumed mutations associated with phenotype B were likely in 3 cats, resulting in false AA or Ab genotyping. To determine if any non-AB blood incompatibilities existed, all of the samples were cross-matched against blood of the same AB phenotype. No conclusive evidence for non-AB blood type incompatibilities were found; phenotyping of all donor and recipient cats is recommended before blood transfusions. Phenotype B cats should have the phenotype confirmed with a repeat phenotype test.


This study represented an introductory and comparative investigation of feline blood phenotyping and genotyping. Feline blood phenotyping is readily available and can be done patient-side. Genotyping will not have practical utility in urgent blood transfusion situations, but it does represent a new avenue for blood typing of blood donors for blood banks and breeding stock in which neonatal isoerythrolysis is a concern. This study has highlighted a high agreement between the two typing methods, while exposing concerns about inaccuracies with phenotyping and genotyping. Also, genotyping has highlighted an increased complexity with regard to mutations. Further investigations across breeds and geographical locations is needed for the type B blood group to address these mutations.—Kelly St. Denis, DVM, DABVP (Feline)


Feline blood genotyping versus phenotyping, and detection of non-AB blood type incompatibilities in UK cats. Tasker S, Barker EN, Day MJ, Helps CR. J SMALL ANIM PRACT 55:185-189, 2014.

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