Animals and
bacteria have cell surface
antigens referred to as a
blood type. Antigens from the human
ABO blood group system are also found in
apes and
old world monkeys, which have inherited the same system. Other animal blood sometimes
agglutinates (to varying levels of intensity) with human blood group
reagents, but the structure of the blood group
antigens in animals is not always identical to those typically found in humans. The classification of most animal blood groups therefore uses different blood typing systems to those used for classification of human blood.