While humans have 8 possible blood types, cats have 3: A, B, and AB. Type A is the most common and Type AB is the rarest.
NOTE: It is possible for Mother’s milk to kill her kittens if the blood types are incompatible. If a female Type B mates with a male Type A, then some of the kittens will most likely be Type A. The milk coming from a Type B cat can kill the Type A kittens. It’s called neonatal isoerythrolysis.
To learn more about feline blood types and neonatal isoerythrolysis, read “Feline blood groups and blood incompatibility“.