This test determines by DNA the alleles of the cat AB blood group system: the A allele (dominant) and the b allele (recessive), which define groups A, b/B and AB. The group determines compatibility in transfusions and, above all, the risk of neonatal isoerythrolysis: a group b queen with anti-A antibodies can destroy the red cells of her group A kittens through colostrum. It is a reproductive management tool rather than a disease test, but its clinical consequences can be fatal for the litter.

Group A is the majority in the general feline population. Group b reaches high frequencies in the British Shorthair, Ragdoll, Birman, Devon Rex and Cornish Rex, and Turkish breeds, with figures that vary by country and line. Group AB is uncommon. For specific breeds, consult the laboratory's data: published frequencies are heterogeneous.

- It is not a disease: a genetic trait with clinical implications\n- Neonatal isoerythrolysis: group A kittens born to a group b mother that stop nursing, weaken and show anaemia in the first 24-72 hours\n- Jaundice, haemoglobinuria and sudden death of kittens in uncontrolled cases\n- Severe transfusion reactions if incompatible blood is transfused\n- Genetic typing guides, but in AB and in Birman cats confirmation by serological methods is advisable

The feline A-b blood group system was established by serological immunology in the mid-20th century, and the uniqueness of the cat was soon understood: many group b queens possess natural anti-A antibodies, which explains the neonatal isoerythrolysis described since the 1960s. The genetics of the system was resolved in the 2000s with the identification of variants of the CMAH gene responsible for groups A and b, which made DNA typing possible from swabs or blood without the need for an immunohematology laboratory. Genetic testing has become standard practice in breeds with a high frequency of group b, such as the British Shorthair and the Ragdoll.

- Type the male and female before mating: know the groups expected in the litter.\n- If the queen is group b and the male is A or AB, plan the birth: separate the kittens from the mother during the first 24 hours and feed them a milk replacer, or mate the b queen only with a b male.\n- Check the group of the at-risk kittens and return them to the mother only when they no longer absorb colostrum antibodies.\n- Record the blood group of each breeding animal in the pedigree: it is also key for future transfusions.

A/b genetic typing by CMAH is reliable for most cases, but the AB phenotype and some uncommon genotypes are better characterised by serological or reference laboratory typing (cross-agglutination). In the face of an urgent transfusion, always perform a compatibility test (crossmatch), also in typed cats. Neonatal isoerythrolysis is a neonatal emergency: anaemia, haemoglobinuria and failure to gain weight in the first 72 hours require immediate action.

1. Giger U et al. 1991, frecuencia y herencia de los grupos A y B en razas felinas (PMID 1997588)
2. Giger U et al. 1996, grupo AB en el sistema felino (PMID 8896680)
3. Bighignoli B et al. 2007, mutaciones de CMAH asociadas al grupo AB felino (PMID 17553163)
4. Gandolfi B et al. 2016, nueva variante de CMAH asociada al tipo AB en Ragdoll (PMID 27171395)
5. Omi T et al. 2016, caracterización molecular de CMAH y el sistema AB felino (PMID 27755584)
6. Kehl A et al. 2018, panel de genotipificación CMAH para tipos A, B y C (AB) (PMID 30235335)
7. OMIA:000119 Grupo sanguíneo felino