Antisera used to identify blood groups (typing reagents) usually are produced as isoimmune sera. Their in vitro serologic characteristics vary with the species. Many reagents are hemagglutinins; others are hemolytic and require complement to complete the serologic reaction, such as in cattle (because RBC do not readily agglutinate) and horses (because RBC rouleaux are a problem). Other typing reagents, neither hemagglutinating nor hemolytic, combine with RBC antigens in an “incomplete” reaction because they lack additional combining sites to agglutinate other RBC; addition of species-specific antiglobulin is required for agglutination.

The diversity of blood groups in animals and the lack of commercially available blood-typing reagents make complete typing and matching difficult but should not preclude the clinical use of transfusions. In horses and dogs, the blood group antigens most commonly implicated in transfusion incompatibilities are known; by selecting donor animals that lack these groups, or that match the recipient, the risk of sensitization of the recipient to the most important antigens can be minimized.

Last full review/revision July 2011 by Susan M. Cotter, DVM, DACVIM (Small Animal, Oncology)