Neonatal Isoerythrolysis

Painted illustration of a weak newborn kitten with its mother

What is it?

Cats have blood types A, B, and the rare AB. Type A is by far the most common, but some pure breeds are more likely to be type B. Type B cats naturally carry antibodies against type A blood. When type A or AB kittens nurse first milk (colostrum) from a type B mother, those antibodies enter the kittens' blood and destroy their red blood cells.

What signs should I watch for?

Kittens look normal at birth but develop severe anemia within two to three days and may die if not treated right away. Signs of anemia include weakness, tiredness, and pale gums.

How is it diagnosed and treated?

Blood tests confirm the diagnosis. Treatment is to stop the kitten from nursing the mother's colostrum, give safe colostrum or a milk replacer, and provide supportive care, including blood transfusions if needed.

Can it be prevented, and what's the outlook?

It can be prevented by blood typing the mother and kittens, withholding risky colostrum, and using colostrum that does not contain harmful antibodies.
The outlook depends on how quickly treatment starts.

Reviewed by the Adler Veterinary Hospital veterinary team, October 2026.

Newborn type A or AB kittens of a type B mother

Who's at risk:

Weakness, tiredness, pale gums in the first days of life

Main signs:

Emergency — see a vet now

Urgency:

When to call a vet right away