Blood types

Blood types (or groups) are determined by specific antigens found on the surface of erythrocytes. In humans, there is the ABO system of blood types, whereas animals have a variety of different blood types. Knowledge of blood types in the different species is important as transfusion of incompatible blood (the donor animal has a different blood type from the recipient animal) can result in severe hemolytic transfusion reactions and even death, in some instances.

There are two types of antibodies to blood group antigens; naturally occurring antibodies and antibodies acquired after exposure to the blood group antigen. Naturally occurring antibodies occur in most species and vary in their pathological significance, i.e. some will not produce a transfusion reaction. Acquired antibodies are produced after exposure to an incompatible blood type, which is from exposure to blood or products containing erythrocytes or their antigens. The most common route of exposure is from previous blood transfusions, however there are less obvious sources of exposure, such as vaccinations that contain foreign red blood cell antigens. Antibodies that are pathogenic (i.e. induce a hemolytic reaction) can cause agglutination and/or hemolysis of red cells.

Blood typing (for the most common blood groups) is offered by a few specialized veterinary diagnostic laboratories (e.g. the Comparative Coagulation Laboratory at Cornell University, the Equine Blood Testing Laboratory in Kentucky, the Stormont Laboratory in California). Ideally, any animal that is routinely used as a blood donor should be blood typed for the most common antigens that produce a hemolytic reaction and (ideally) should be negative for these antigens. Blood type compatibility (or incompatibility) is determined in the laboratory using crossmatching procedures. Since administration of typed negative blood will not prevent a transfusion reaction to less well-characterized red cell antigens, crossmatching should always be performed in an individual that has been previously exposed to blood group antigens.

Canine blood groupsFeline blood groups
Equine blood groups Misc. blood groups