Cats have one blood group system, the feline AB blood system that is characterized by three blood types: type-A (as the most common), type-B (less common) and type-AB (extremely rare).
Distribution of the feline blood types
Distribution of the feline blood types source: Icatcare
The distribution of feline blood types is defined by two factors:
- Geographic region
Blood group A is the most common blood type among domestic cats in all countries of the world. Blood group B has its highest frequency in Northern Asia and neighboring Central Asia, and its incidence diminishes both towards the west and the east, falling to single digit percentages in Spain. The AB blood type is very rare.
Breeds with only type A or a low frequency of type B (<10%) include:
- American Shorthair
- Maine Coon
- Norwegian Forest
- Oriental Shorthair
Breeds with an intermediate frequency of type B cats (10-25%) include:
Breeds with a high frequency of type B cats (>25%) include:
- British Shorthair
- Devon Rex
- Turkish Angora
Why are feline blood types important?
Unlike other mammals, cats are capable of producing naturally occurring antibodies against the blood group they lack. Natural means that there is no need for previous exposure to either blood or blood products. Cats of blood type-B have strong antibodies against type-A cells, while cats of blood type-A have weak antibodies against type-B cells.
Young kittens have no antibodies against other blood groups during the first week of life. Only kittens older than three months have natural occurring antibodies against other blood groups. The antibodies are usually produced as a result to exposure to antigens on bacteria, plants or protozoa that are structurally similar to the red cells’ antigens.
Feline Neonatal Isoerythrolysis (FNI)
Definition and significance
FNI is a fatal, hemolytic condition caused by blood type incompatibility between the mother and baby’s blood type. FNI is characterized with immune-mediated destruction of red blood cells.
FNI is listed as the leading cause of the “fading kittens syndrome’’. It is believed that FNI is more common than recognized in the practice and the associated mortality rate is high.
FNI occurs relatively rare among non-pedigree cats, but can be quite common in specific cat breeds.
FNI develops when there is a blood type mismatch between the two mating cats. More specifically, when type-B queens mate with type-A or AB tomcats. In that case, some of the newborn kittens will be type A, some will be type B and some will be type AB.
Since the feline placenta does not allow passage of maternal antibodies, kittens receive their mother’s antibodies when suckling the first milk (colostral milk). Because the mother is type B, she has anti-A-antibodies. When the type-A and AB kittens absorb the anti-A-antibodies from their mother, they cause blood incompatibility reaction that results in massive and often fatal erythrocyte destruction. Death usually occurs after few hours to two weeks of age.
It should be noted that FNI does not occur in type B kittens born to a type-A queens, as type-A cats have either extremely low levels of antibodies against the type-B blood cells or no antibodies at all.
Depending on the colostral antibody uptake, the clinical signs can range from unapparent to severe hemolytic anemia.
Generally the kittens are born healthy and nurse energetically. The first symptoms occur after the colostrum ingestion. They include:
- Stopped or decreased suckling
- General weakness
- Dar red-brown urine
As the condition progresses, the symptoms include:
- Pale mucous membranes
- Increased heart rate
- Increased respiratory rate
Some kittens may suddenly die without showing any previous signs. In mild cases of FNI, the affected kittens suffer from gradual dying of the ear tips and tail tips. Necrotized ear and tail tips are also common in kittens that survived FNI.
The diagnosis is based on the queen’s history and the presenting clinical signs by the kittens. The diagnosis is confirmed by blood typing the queen and the kittens. If blood typing is not possible, a blood cross-matching can be performed. Kittens with FNI present a positive Coomb’s test. If FNI is suspected all kittens should be blood typed at birth by using cord blood.
FNI requires immediate and aggressive treatment. When the first clinical signs appear, type-A or AB kittens should be immediately removed from their mothers, while type-B kitten can continue to suckle. Affected kittens may be transfused with 5-10 mL washed type-B red cells via intravenous or intra-osseous catheter.
In an A or AB blood kitten with FNI, the queen’s circulating colostral antibodies are anti-A, so the only alloantibodies present in the newborn kitten are the anti-A-antibodies. Therefore transfusion of type-A cells simply adds more vulnerable cells to the kitten’s circulation. Therefore the best blood donor would be the queen as she cannotreact to her own antibodies.
However, since kittens start to produce their own anti-B-antibodies few days after birth, if a further transfusion is necessary, type-A blood is to be used.
Unfortunately, because of the sudden onset and acute nature of the disease, in most cases the therapy is unsuccessful.
As with any other preventable condition, when it comes to FNI it is better to be safe than sorry. Therefore, the best way to prevent FNI is to blood type the progenitors, mostly those belonging to breeds with high incidence of type-B blood individuals.