Cats have three blood types: A, B, and AB. These belong to a single classification called the AB blood group system, which is the primary blood group system recognized in cats. Unlike humans, who have four common types across the ABO system, feline blood typing is simpler in number but carries surprisingly high stakes when it comes to transfusions and breeding.
The Three Feline Blood Types
Type A is by far the most common blood type in cats. The vast majority of domestic cats, particularly mixed-breed cats, are type A. Type B is the second most common, though its prevalence varies significantly by breed and geographic region. Type AB is rare across all breeds and regions.
Blood type in cats is inherited through a straightforward genetic pattern. The A type is dominant over B, meaning a cat only needs one copy of the A gene from either parent to be type A. A cat must inherit the B gene from both parents to be type B. The inheritance pattern for the rare AB type isn’t fully understood yet, but it appears to function as a separate trait rather than a simple combination of A and B.
Which Breeds Are More Likely to Be Type B
While type A dominates the general cat population, certain purebred cats carry type B at much higher rates. Breeds like the British Shorthair, Devon Rex, Cornish Rex, and Turkish Van have notably elevated rates of type B. In some of these breeds, a significant portion of the population carries type B, making blood typing before any medical procedure especially important for purebred cats. Geography also plays a role: type B prevalence among non-pedigree cats differs between regions, with some areas of Europe and Australia showing higher rates than North America.
Why Cat Blood Types Matter More Than You’d Expect
What makes feline blood types medically critical is something cats share with very few other animals: they are born with naturally occurring antibodies against the blood type they don’t have. A type B cat already has strong anti-A antibodies circulating in its blood from birth, without ever being exposed to type A blood. About one-third of type A cats carry weaker anti-B antibodies. Type AB cats, interestingly, produce neither anti-A nor anti-B antibodies, making them universal recipients for transfusions.
These preexisting antibodies mean a cat can have a severe, potentially fatal reaction to its very first mismatched transfusion. This is different from dogs, where a first mismatched transfusion is less likely to cause an immediate crisis. In cats, the danger is immediate. A type B cat receiving type A blood can experience rapid destruction of the transfused red blood cells, leading to shock and death within minutes to hours. The reaction in the reverse scenario (a type A cat receiving type B blood) is generally less severe but still harmful, causing the transfused cells to be destroyed within hours or days.
Transfusions Require Both Typing and Crossmatching
Because of these naturally occurring antibodies, veterinary guidelines call for both blood typing and crossmatch testing before a cat receives any transfusion, even its first. Crossmatching mixes a small sample of the donor’s blood with the recipient’s blood in the lab to check for a reaction. This extra step catches incompatibilities that blood typing alone might miss, particularly since additional blood group factors beyond the AB system (such as a lesser-known antigen called Mik) may also cause reactions in some cats.
In-clinic blood typing can be done using rapid test cards or cartridges that give results in minutes. These point-of-care tests are generally reliable, with accuracy rates above 98% when results are interpreted correctly. A more traditional lab method, tube agglutination, is considered the gold standard but takes at least an hour and requires more training to perform. Newer gel-based tests offer a middle ground: faster, more standardized, and producing stable results that can be reviewed for days afterward. However, gel tests occasionally produce ambiguous patterns that need a second method to confirm.
Blood Type Conflicts in Newborn Kittens
Blood type incompatibility doesn’t only matter during transfusions. It can also affect newborn kittens through a condition called neonatal isoerythrolysis. This happens when a type B mother gives birth to type A kittens (which occurs when the father is type A). The mother’s milk, particularly the colostrum produced in the first day after birth, is rich in her anti-A antibodies. When type A kittens nurse, they absorb those antibodies through their gut, and the antibodies attack the kittens’ own red blood cells.
Affected kittens may seem healthy at birth but quickly become weak, stop nursing, and develop dark or discolored urine as their red blood cells break down. Some kittens die within the first few days of life. Others survive but may lose the tip of their tail or ear tips due to small blood clots. Breeders working with breeds that have higher type B rates often blood-type their breeding cats specifically to avoid this pairing. If the mating does produce at-risk kittens, removing them from the mother for the first 16 to 24 hours and bottle-feeding them can prevent the antibodies from being absorbed.
Should You Know Your Cat’s Blood Type?
For most cat owners, blood typing isn’t something you need to arrange proactively. Your vet will type your cat’s blood before any transfusion or surgery where transfusion is a possibility. But if you breed cats, especially purebreds with known type B prevalence, knowing the blood types of both parents is essential to prevent neonatal isoerythrolysis. Some breeders include blood type testing as a routine part of their health screening alongside genetic tests for heart disease and other conditions.
If your cat has a chronic illness that might eventually require a transfusion, such as kidney disease or certain cancers, having the blood type on file in advance can save valuable time in an emergency. Blood typing requires only a small blood sample and is widely available through veterinary clinics and reference laboratories. The UC Davis Veterinary Genetics Laboratory, for example, offers a DNA-based test that determines blood type from a cheek swab, which can be useful for breeders testing kittens or cats that are difficult to draw blood from.