[BLOG] Blood groups in feline: 8 facts about [AB]

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Last month, I had the opportunity to lecture at the World Cat Congress in Miami. Two reasons I was glad I could that: 1st/ I knew I would lecture to a group of passionate people, and nothings is better in order to have great discussions and 2nd/ it was in Miami, it was +27ºC while when I left Toronto it was -20… My topic: Colostrum and kitten’s immunity (you can see my slides here)

• Three blood groups to consider in the feline species

Remember, there are 3 blood groups in cats: [A], [AB] and [b]. We usually speak a lot about [A] and [b]. But what about [AB]? Apart from the fact that “it is rare”, must admit this is not something I usually discuss. I have a slide I often use which shows that individuals from the [AB] group do not produce antibodies against [A] red cells nor [b]’s. But usually, again, because “it is rare”, that where the discussion ends.

I promised myself I would look into it. So when I got back home, I went back to the books (always a good thing to do when you question yourself!). Here is what I found on this [AB] group, might answer some questions feline breeders have!

Fact #1: The [AB] blood group is NOT a genetic mix between the alleles A and b. In fact it is a totally different allele (we might even have to change its name one day to avoid any confusion!). In terms of genetic determinism, we are therefore dealing here with 3 DIFFERENT alleles. The AB allele is recessive to the A allele, but dominant over b.

• [AB]: not a common blood group in feline populations  

Fact #2: As you can see on the table below, it is indeed rare to find [AB] individuals. That explains why we tend to omit it when discussing feline blood groups.

from Knottenbelt, 2011 see here for reference

Fact #3: A blood group antigen is a protein that is carried by the red cells (that can eventually trigger an immune response). Red cells of cats from the [A] group carry type-A antigens, while red cells of cats from the [b] group carry type-b antigens. Red cells of [AB] individuals carry both type-A AND type-b antigens.

Fact #4: Tests we usually use in-house at the vet clinic generally detect those type-A and/or type-b antigens. As we said, [AB] individuals carry both: the cat is therefore [AB] when the test is positive for both antigens.

• [AB]: about blood transfusion and neonatal erythrolysis

Fact #5:  [A] cats usually have low levels of anti-b antibodies, while [b] cats have high levels of anti-A antibodies. [AB] individuals have no antibodies neither against type-A or type-b antigens.

Fact #6: Since [AB] cats have no both express type-A and type-b antigens AND that they have no anti-A nor anti-b antibodies, these cats are in theory universal recipients when it comes to blood transfusion. In different studies, blood transfusion of [A] or [b] red cells in [AB] individuals did not lead to any adverse reaction. It has however been recently suggested that [AB] cats should only receive [A] or [AB] red cells. Indeed, the serum of [b] individuals still contains antibodies directed against type-A antigens (which [AB] red cells carry). In these cases, a immune reaction might still be triggered.

Fact #7:  Because [AB] red cells carry the type-A antigen, neonatal erythrolysis can also occur in [AB] kittens receiving the milk of a [b] queen.

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