<P> The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes . In human blood transfusions it is the most important of the 36 different blood type (or group) classification systems currently recognized . A very rare (in modern medicine) mismatch in this, or any other serotype, can cause a serious, potentially fatal, adverse reaction after a transfusion, or a contra - indicated immune response to an organ transplant . The associated anti-A and anti-B antibodies are usually IgM antibodies, which are produced in the first years of life by sensitization to environmental substances, such as food, bacteria, and viruses . </P> <P> The ABO blood types were discovered by Karl Landsteiner in 1901, for which he received the Nobel Prize in Physiology or Medicine in 1930 . ABO blood types are also present in some other animals such as rodents and apes, including chimpanzees, bonobos, and gorillas . </P> <P> The ABO blood types were first discovered by an Austrian Physician Karl Landsteiner working at the Pathological - Anatomical Institute of the University of Vienna (now Medical University of Vienna). In 1900, he found that blood sera from different persons would clump together (agglutinate) when mixed in test tubes, and not only that some human blood also agglutinated with animal blood . He wrote a two - sentence footnote: </P>

Who figured out a way to determine the type of blood