Just as with humans, cats have several different possible blood types, or “serotypes”: A (genotype N/N), B (genotype b/b) and AB (genotype N/b). The cat’s immune system produces antibodies that attack cells with the opposite serotype; e.g. a cat with Serotype A produces antibodies agaisnt Serotype B, and a cat with Serotype B produces antibodies against Serotype A. A cat with Serotype AB produces neither.

This means that a cat cannot recieve a blood transfusion from a cat with another serotype, as this would cause a dangerous and likely fatal reaction. These antibodies are also produced in a female cat’s milk, and will attack kittens of the opposite serotype (known as Neonatal Isoerythrolysis), which is also often fatal. A Serotype B mother has produces especially strong antibodies against Type A.

It is therefore important to match donor and recipient serotypes, and ensure that breeding pairs will result in kittens with the same serotype as their mother.