Blood type (A, B, AB) in cats

Cats have three main blood types: A, B and AB. Unlike dogs, cats carry ready-made antibodies against the type they lack, so the wrong blood can cause a severe reaction even at a first transfusion. The type matters for kittens too: a type B mother passes antibodies against type A through her colostrum.

SectionComplete blood count

SampleWhole blood with EDTA (purple-top tube); not frozen

Units—

On formsA/B/AB

What it shows

The main blood group system of cats is called AB, and it has three types: A, B and AB. They are set by sugar-based markers on the surface of red blood cells. The type is inherited, with A dominant over B; how type AB is inherited is not known. Most cats are type A, and AB is rare.

What makes cats different from dogs is that they carry ready-made antibodies against the type they do not have, without ever having had a transfusion. In type B cats the anti-A antibodies are strong; in type A cats the anti-B antibodies are weaker. So the wrong blood can cause a serious reaction at the very first transfusion.

Besides the AB system there are other red cell markers — Mik, and five groups named FEA 1–5 described in 2021. AB typing does not detect them.

Higher than reference — what it may be a sign of

Type A — the most common type. Some type A cats have anti-B antibodies: in a type A cat, half of transfused type B cells are gone in about two days on average, against about a month for matched blood; signs are milder.
Type B — the cat has strong anti-A antibodies. In a type B cat, half of transfused type A cells are destroyed in about 1.3 hours on average, and the reaction can be life-threatening. A type B queen also passes these antibodies into her colostrum — see the cat section below.
Type AB — rare. Such cats have no natural antibodies against A or B.

No type is a sign of illness; the type matters for a transfusion and for kittens.

Lower than reference

A blood type has no “low” result. What matters here is what typing cannot see. Antibodies against Mik are not detected by AB typing, and antibodies to FEA groups can appear as soon as 5 days after a first transfusion. That is why a crossmatch is advised in cats even if the type is known, and in cats it is recommended more than 2 days after any earlier transfusion, whatever their transfusion history.

Look at together with

Crossmatch — the cat’s and the donor’s blood are mixed to look for a reaction. It also catches incompatibility outside the AB system, and in an emergency it is how compatibility is checked when there is no time to type.
Haematocrit and hemoglobin — show how marked the anemia is; anemia is what most often leads to a transfusion.
Blood type in dogs — dogs have a different system and no ready-made antibodies against their main group.

Units and conversion

There is nothing to convert here: the form simply names the type — A, B or AB. Clinics usually check it with a card or a strip (immunochromatographic) kit; on a strip, a control line “C” shows that the test itself worked. Results of such kits agree well with laboratory methods. The app keeps the type as text.

Reference range

On your lab’s form you will see a type, not a range: A, B and AB all occur in healthy cats. In cats, typing before a transfusion is considered essential — before the first one too, and in cats of every breed — and a cat is given blood of its own type: A to A, B to B. The vet chooses the donor and the blood product.

Cats and dogs

Cats

How common type B is depends on breed and region. The sources list no type B in Siamese and related breeds, Burmese, Tonkinese and Russian Blue, and 20–45% type B in Exotic and British Shorthair, Cornish and Devon Rex. Type B queens mated with type A or AB toms can have type A or AB kittens at risk of neonatal isoerythrolysis: during the first 24 hours the kittens absorb anti-A antibodies with colostrum and their red cells are destroyed. Affected kittens may weaken, turn pale and jaundiced, stop nursing or pass red urine; some show no signs.

Dogs

Dogs have a different set of blood groups, named DEA, with DEA 1 the most important. Unlike cats, dogs usually have no ready-made antibodies against DEA 1, so a crossmatch is not required before a dog’s first transfusion — see blood type in dogs.

In the app

Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.

Open the app

Sources

Updated 6 November 2026 · Mihail Ivanov, creator of Pet Tracker Space · Written with Claude and checked against the sources above.

This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.