* This test detects the c.268T>A variant corresponding to Type B in most cats
** For Ragdolls and Turkish breeds, see the complete panel

Gene affected: CMAH
The A allele is dominant to the b allele
Thus, the following genotypes can be observed: 
A/A, A/b et A/ac for group A
b/b for group B

OMIA link: 000119-9685
Breeds: Several breeds
Description:
In domestic cats, the blood system includes three types: A, B, and C (also known as AB), which vary in frequency across breeds and geographic regions. Kehl et al. 2018 reports that of 421 phenotypically typed cats, 60% were A, 35% B, and 5% C.
Siamese, Tonkinese, and Burmese breeds are nearly fixed for type A, while the prevalence for type B in British Shorthairs, Birmans, Devon, and Cornish Rex can vary between 25% and 50%. (Giger and Bucheler, 1991). Although type B cats are rare in randomly bred populations, mixing with other breeds of cats increases the frequency of type B cats in this population.

Breeding strategy:
Avoid mating b allele carriers with other 'b' carriers to avoid obtaining serologically B kittens.
Blood group B cats should only be bred to group B cats.

See the Labgenvet website for more details:
Blood Group AB, blood types A, AB, B and the alleles A, aAB, and b in the cat
Cat genetic profile - Feline blood group
References:
Kehl, A., Heimberger, K., Langbein-Detsch, I., Boehmer, S., Raj, K., Mueller, E., Giger, U. :    
Molecular characterization of blood type A, B, and C (AB) in domestic cats and a CMAH genotyping scheme. PLoS One 13:e0204287, 2018. Pubmed reference: 30235335. DOI: 10.1371/journal.pone.0204287.
Gandolfi, B., Grahn, R.A., Gustafson, N.A., Proverbio, D., Spada, E., Adhikari, B., Cheng, J., Andrews, G., Lyons, L.A., Helps, C.R. (2016) A novel variant in CMAH is associated with blood type AB in Ragdoll cats. PLoS One 11:e0154973, 2016. Pubmed reference: 27171395. DOI: 10.1371/journal.pone.0154973.
Giger, U., Bucheler, J., Patterson, D.F. (1991) Frequency and Inheritance of A and B Blood Types in Feline Breeds of the United-States Journal of Heredity 82:15-20, 1991. Pubmed reference: 1997588.