Feline blood types: What you need to know and why (Proceedings)


Feline blood types: What you need to know and why (Proceedings)

Aug 01, 2010

Feline Blood Groups

There are three well-known, clinically important blood groups in cats: A, B, and AB.1-2 Despite the nomenclature, the antigens in the feline AB blood group are not serologically related to the human ABO blood group antigens. Another potentially important group called MiK has recently been identified.3 The blood groups are genetically determined species-specific red blood cell surface antigens. The A-allele is dominant over the b-allele so that cats with genotypes A/A and A/b will be type-A, while only the homozygous b/b will have the type-B phenotype. A third type, AB, occurs rarely and expresses both the A and B antigens.4 However, the heritability of type-AB is not well understood.

Various methods are now available to determine blood type, both in a referral laboratory setting and patient-side. Diagnostic laboratories use various serological methods based on agglutination reactions. In addition, genetic testing is now available to identify blood types A and B using buccal swabs, although it cannot distinguish between A and AB blood groups.5 Patient-side testing may be performed with a card typing system (RapidVet®-H, DMS Laboratories, Flemington, NJ). If the card-typing system is used, type-AB and type-B results should be confirmed by a referral laboratory as some cross-reactions have been known to occur.6 A recently introduced option for patient-side blood typing is the gel column agglutination test (DiaMed-Vet® feline typing gel, DiaMed, Switzerland). This test is easier to interpret than the card method, although it requires a specially designed centrifuge that may be cost-prohibitive in some settings.7 An evaluation of various blood typing methods for the cat concluded that the gel column test is reliable when compared to the gold standard Penn tube assay.6

Table 1: Selected Blood Type A and B Frequencies in Cats (ignoring AB blood types)
The distribution of feline blood types varies by geographic region and breed (Table 1).8-9 Type-A is the most common type among most cats. There is, however, geographic variation in the prevalence of type-B domestic shorthaired cats. Over 10% of the domestic shorthair cats in Australia, Italy, France and India are type-B. Breed distribution does not vary as much by location because of the international exchange of breeding cats. Over 30% of British Shorthair cats, Cornish and Devon Rex cats, and Turkish Angora or Vans have type-B blood. In contrast, Siamese and related breeds are almost exclusively type-A. Ragdoll cats appear to be unique with regard to blood types. Approximately 3.2% of Ragdoll cats are discordant for blood group when genotyping is compared to serology, necessitating further investigation in this breed.9

The AB blood type is very rare while the frequency of the MiK blood type is unknown. The presence of red blood cell antigens in addition to the AB group may explain why transfusion compatibility is not guaranteed by blood typing; crossmatching is recommended prior to any transfusion.3 Breeding queens, along with blood donors and, if possible, blood recipients should be blood typed.

Understanding feline blood groups is important because, unlike other mammals, cats produce naturally occurring antibodies, called alloantibodies, against the red blood cell antigens not present on their own cells. The kitten produces these alloantibodies around two to three months of age resulting from the exposure to antigens on plants, bacteria or protozoa that are structurally similar to the red cell antigens. No alloantibodies are produced against antigens that are similar to self-antigens and no previous exposure to blood products (e.g., transfusion or pregnancy) is necessary to produce the alloantibodies. Type-A cats may have low levels of naturally occurring antibodies against blood type-B red cells, but all type-B cats have high levels of naturally occurring anti-A antibodies. Blood type-AB cats do not have alloantibodies.