All blood transfusions between cats require blood types to be matched, otherwise fatal transfusion reactions can occur. Blood typing for transfusion can safely be carried out using serological (non-genetic) methods. However, for breeders the main concern regarding blood types is identifying blood type B cats, in particular breeding queens. To be blood type B, a cat must have two copies of a recessive b allele. Genetic
testing has an advantage over serological testing because it can identify blood type A or AB cats that have one copy of a b allele (termed carrier of b). These cats would be reported as type A by conventional (serological) blood typing methods, which cannot detect the carried b allele, but mating two such cats together can result in blood type B kittens being born. This is not a risk to the kittens when born but can affect future mate compatibility when breeding from them in the future.