DEFINITION AND CLASSIFICATION
Three blood groups, named A, B and AB, have been described in the cat. Cats have naturally occurring isoantibodies against the antigen not present on the surface of red blood cells.
From a genetic point of view, the A antigen is dominant with respect to the B antigen; for this reason, subjects with group A can be homozygotes (A/A) or heterozygtes (A/B) while those with group B are always homozygotes (B/B). The mechanism of inheritance underlying the appearance of group AB is not clear, although it does not derive from co-dominance of types A and B. The AB allele is recessive with respect to the A allele and dominant with respect to the B allele.
Group A is the most common type of blood. Its incidence in the domestic cat varies depending on the geographical location: in Italy it is the blood group of about 88.8% of European cats. Subjects with this blood group have a low titre of anti-B antibodies (IgG and IgM), which have both haemagglutinating and haemolytic effects. If a cat is transfused with type B red blood cells, the half-life of the cells will be about 2 days. Minor transfusion reactions can be observed, characterized above all by extravascular removal of the red blood cells; these reactions are sometimes not clinically evident.
Group B is less common. Its incidence in the domestic cat also varies depending on the geographical location: in Italy it is 12.2%. Group B is more frequent in the following breeds: Abyssinian, Birman, Persian, Sphynx, Devon Rex, Cornish Rex, Exotic and British Shorthair, Turkish Van and Turkish Angora. Subjects with this blood group have a high titre of anti-A haemagglutinins and haemolysins. A severe, potentially fatal reaction occurs if a type B subject is transfused with type A red blood cells. The red blood cell destruction is intravascular and occurs in a short time.
GroupAB is very rare. It has been observed in short-haired and long-haired domestic cats and in the following breeds: Abyssinian, Birman, British Shorthair, Norwegian Forest Cat, Persian, Scottish Fold, Cornish Rex, Devon Rex, Maine Coon, Manx, Ragdoll, Sphynx, Bengalese, Egyptian Mau and Siberian. Subjects with this blood group do not have naturally occurring anti-A and anti-B isoantibodies.
Given the presence of natural isoantibodies in the cat, it is essential that the blood groups of donor and recipient cats are determined before carrying out a transfusion in order that the transfusions are between compatible subjects and that transfusion reactions do not, therefore, occur.
One important problem that can be found in clinical practice is neonatal isoerythrolysis which occurs when a type A or AB kitten is born from a type B female mated with a type A or AB male. The mother’s colostrum will contain large amounts of anti-A antibody which can be the cause of a severe haemolytic anaemia in the kitten. The blood groups of the tomcat and queen would have to be typed, to determine their compatibility, prior to mating in order to be able to prevent the development of neonatal isoerythrolysis.
Another red blood cell antigen, called Mik, and its corresponding alloantibody have been described recently. The type of hereditary transmission, frequency, geographical distribution and molecular characterization of this antigen are yet to be determined.
Since there is not a universal feline donor, all cats must be typed and/or undergo cross-matching before receiving a transfusion. Subjects with group AB blood are considered “universal recipients” and can receive both type A and type AB blood. However, since type B blood contains large amounts of anti-A antibodies which could cause haemolysis, it is better to choose a type A or type AB donor for group AB recipient cats.
BLOOD GROUP TYPING
Blood group typing is usually based on serological studies involving the agglutination reaction. Since there are natural antibodies in cats, the blood groups must always be typed before carrying out a transfusion. The methods that can be used to type the blood group include kits involving rapid agglutination on card (Fig. 1), agglutination in test-tubes and agglutination in columns of gel (Fig. 1). The typing is carried out on samples of whole blood collected into K3EDTA. Particular care must be taken in the presence of agglutination. In these cases, the red blood cells from the cat to be typed must be washed three times in physiological saline. If the red blood cells remain clumped it will not be possible to type the blood group.
Suggested readings
- Day HJ, Mackin A, Littelwood JD Ematologia e medicina trasfusionale del cane e del gatto. Ed. UTET, 271-316, 2004
- Giger U, Blais MC, Atti del 23° Congresso ACVIM di Baltimora, 2005
- Hohenhaus AE, Importance of blood groups and blood group antibodies in companion animals. Transf. Med. Rev., 18, 117-126, 2004
- Knottenbelt CM, The feline AB group system and its importance in transfusion medicine. J. Fel. Med. And Surg. 4, 69-76, 2002
- Lanevschi A, Wardrop KJ, Principles of transfusion medicine in small animals. Can. Vet. J., 42, 447-454, 2001
- Wardrop KJ, Reine N, Birkenheuer A, Hale A, Hohenhaus A, Crawford C, Lappin MR, Canine and feline blood donor screening for infectious disease. J. Vet. Intern. Med., 19, 135–142, 2005
- Weinstein N, Blais MC, Harris K., Oakley DA, Aronson LR, Giger U, A newly recognized blood group in domestic shorthair cats: the Mik red cell antigen. J. Vet. Intern. Med., 21, 287–292, 2007
- Weiss DJ, Wardrop J Schalm’s Veterinary Hematology 6th edition. Ed. Wiley-Blackwell, 711-756, 2010