Blood Types in Cats
Humans have four main blood types: A, B, AB, and O. Do cats also have similar blood types? They do! Here's the lowdown on feline blood types:
Cats have 3 blood types, the same ones as humans, except for O. There is no universal feline blood donor. Most cats have type A blood, which is also the most common type in humans.
Blood type is determined by the cat's genetic heritage. Due to fewer tests being done on cats than on dogs, it was 2007 before the genetic factors that determine a cat's blood type were identified!
And just as humans can be positive or negative for an Rh factor in their blood, cats have additional blood antigens. Cats are either positive or negative for these antigens in their blood; more on this below.
Some purebred cats are more likely to have type B blood. Approximately half of the Turkish Angora cats tested in one study were type B, 41% of both Cornish and Devon Rexes, and a third of British Shorthair cats. Another study by the University of Pennsylvania found 59% of British Shorthairs were type B, 49% of Devon Rexes, and a third of the Cornish Rexes.
There also seems to be a geographical correlation with type B blood: it runs through the veins of a higher percentage of the cats tested in Australia (26-36%), Turkey (25%), India (12%), France (15%), Italy (11%)...and London, England (31%) (but not as much so in England outside of London, which had only 3% type B cats). Within the United States, the highest percentage of cats with type B blood seems to be in the Pacific northwest - but that's only 6% of cats there.
Only rarely do we encounter a cat with type AB blood. The UPenn study referenced above found cats with AB blood type within a few breeds: British Shorthair, Ragdoll (from Italy), Scottish Fold, Somali, and Sphynx.
What Difference Does Blood Type Make in Cats?
People who have type A blood can only receive transfusions from others with type A. B-type only from B-type. Those with type AB can receive blood from any other type. Human type O is also known as the universal donor, because all blood types can receive type O blood.
It is the same in cats. If your veterinarian needs to give kitty a transfusion, there must be a donor cat on hand who has the same type of blood. Otherwise, the cat's body would reject the cells in the donated blood as being foreign invaders. This would cause serious health problems that could be fatal.
But cats are also unique among mammals, in that most of them produce a type of antibody that will attack the red cells of blood introduced to their system if its type differs from their own. These are known as alloantibodies. Kittens begin producing alloantibodies at about 8-12 weeks of age.
The Mik factor is a type of alloantibody only discovered in this century. Others that have been identified are IgG and IgM. Again, because there have been less studies done on cats than on dogs, less is known about additional alloantibodies that may be as yet undiscovered.
Cats with type B blood have an especially high number of alloantibodies. They should not under any circumstances receive any amount of type A blood, as it could be fatal. Cats with type AB blood produce no alloantibodies and may receive blood from either A or B blood-type cats.
In breeding cats, blood type is also an important consideration. If a female cat has type B blood and is bred to a male with type A, any kittens born with type A or AB blood may not survive. They develop a condition known as neonatal isoerythrolysis (NI), or fading kitten syndrome. This is due to the colostrum in the mother's milk that is designed to protect them from diseases during their first 24 hours of life. Because of the higher number of alloantibodies in her type-B blood, they will attack the blood of any kittens with an A in their blood type and kill them, as well.
If a queen has type B blood and is bred to a tom with type A or AB blood, it may be advisable to separate the kittens from her for the first 24 hours in case they are of blood type A. They could be bottle-fed or nursed by another lactating queen who has blood type A. This would be especially important in the breeds mentioned above with a higher tendency toward having type B blood.
Are There Blood Banks for Cats?
There are! However, most cats must be anesthetized for them to donate blood, so they are far less common than those for dogs. Most veterinarians have another cat in their clinic who can donate a small amount of blood for a kitty who needs it.
As with human blood stored in banks, donated feline blood must be handled and stored carefully to prevent contamination and remain useful. It can be stored for up to a month, but should be used as soon as possible after donation. Naturally, donor cats are screened prior to donation to make sure they are free of diseases such as FeLV and FIV, have been vaccinated against rabies, and are indoor-only cats in good health.
Nine Lives Blood Services in Michigan was the nation's first such feline blood bank. Their donor cats come from nearby shelters. Staffed by a veterinarian and a licensed veterinary technician (LVT), the blood bank doubles as a cat rescue facility that helps place shelter animals into homes.
The University of Pennsylvania maintains a feline blood bank where cat donors are kept for three years, then adopted into homes. The Ohio State University's Veterinary Medical Center keeps a list of available nearby feline blood donors on hand, to which they offer several free perks for enrolling that not only reward the donor kitties, but help keep them healthy.
Is Cat Blood Different From Human Blood?
Yes, cat blood and human blood are different. A cat cannot accept a transfusion from a human, and vice-versa, even if they are both of the same blood letter-type.
How Do I Know My Cat's Blood Type?
Veterinarians and labs use several methods to test a cat's blood for type. There is currently no home-testing kit to determine your cat's blood type. Vets who are testing cats for transfusions or organ donation must also test for alloantibody types present in each cat's blood, as these may cause rejection of blood or an organ if they are not matched that would likely be fatal to the recipient.
Sources: "Feline Blood Types: What you need to know and why (Proceedings)" on DVM360; "A Newly Recognized Blood Group in Domestic Shorthair Cats: The MiK Red Cell Antigen" on the National Institutes of Health's U.S. National Library of Medicine (March-April, 2007, pages 287-292); "Feline Blood Types (Transfusions and Neonatal Isoerythrolysis)" on the Winn Feline Foundation (2015); "Blood Donor Cats: Offering your cat to be used as a blood donor" on International Cat Care.