Dog and Cat Blood Types

It’s well known that people have different blood types and the same is true in animals.

What is a ‘blood type’?

A blood type refers to the presence, absence or variation of chemicals on the surface of red blood cells. Just as animals have different coloured eyes or hair due to different chemicals, they have different blood types.

  • In dogs, more than a dozen blood types have been identified!
  • In cats there have been two blood groups described but there
    are likely to be many more

Although many different blood types exist, in veterinary practice we only tend to be concerned with one group in dogs and one group in cats.

DEA 1.1

Canine blood types: Dogs can either be DEA 1.1 negative or positive. Negative dogs recognise the blood from positive dogs as foreign and can react against it

What is the blood type system in dogs?

The blood type system that we commonly test for in dogs is called Dog Erythrocyte Antigen (DEA) 1.1.

This blood type can either be:

  • present (DEA 1.1 positive)
  • or

  • absent (DEA 1.1 negative)

What happens if a dog receives blood of a different type to their own?

The reason blood types are considered important is that there is a split in the canine population with about half being DEA1.1 positive and half being DEA 1.1 negative. The immune system of DEA 1.1 negative dogs recognises DEA 1.1 as a foreign substance and so attacks it. This can lead to severe transfusion reactions if a DEA 1.1 negative dog is given blood from a DEA 1.1 positive donor.

Just like in most illnesses, the immune system takes longer to react the first time it encounters something and so there is unlikely to be an immediate problem if a dog receives a mismatched blood transfusion the first time.

If a DEA 1.1 mismatched transfusion happens for a second time, the immune system is already prepared for the foreign substance and so the reaction can be quite severe, even life threatening.
Cat blood groups

Feline blood groups: Cats can be A, B or AB and have antibodies against the other blood types meaning that fatal reactions can occur if their blood is mismatched

What is the blood type system in cats?

The situation in cats is a little different as the most important blood group in this species is the AB system. Cats can either be:

  • type A
  • or

  • type B
  • or

  • type AB

This means that their red blood cells have either the A antigen (an antigen is a surface chemical), B antigen or both. Confusingly, these are not the same as the AB blood types in people and cats do not have a type O.

What happens if a cat receives blood of a different type to their own?

Similar to dogs, mismatched blood transfusions can lead to life threatening reactions but the situation is a little different as the immune system in cats is pre-prepared and can react badly the first time there is a mismatch.
neonatal isoerythrolysis

Antibodies can be transmitted in milk, putting kittens at risk if they are a different blood type from their mother

Even a few drops of AB mismatched blood to a cat can be fatal. This is also important when breeding cats as kittens with type A blood can have a fatal reaction (called neonatal isoerythrolysis) if they drink milk, containing antibodies, from a type B queen.

What is ‘crossmatching’?

Another term you may hear in reference to blood types is ‘crossmatching’.

Crossmatching is a blood test that is used to test a patient’s immune system to make sure it is not going to attack the red blood cells from a donor that it may be about to receive due to incompatible blood types.

In small animal veterinary medicine, crossmatching is usually done for blood transfusions more than 5 days after a patient’s first ever transfusion, as after this time there is an increased risk of reactions against the less common blood types that we don’t usually test for.

Although crossmatching is very important to prevent this particular type of reaction (known as an “acute haemolytic transfusion reaction”), many other types of transfusion reaction can occur which cannot be predicted/prevented.