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History

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:

The serum of healthy human beings not only agglutinates animal red cells, but also often those of human origin, from other individuals. It remains to be seen whether this appearance is related to inborn differences between individuals or it is the result of some damage of bacterial kind.

This was the first evidence that blood variation exists in humans. The next year, in 1901, he made a definitive observation that blood serum of an individual would agglutinate with only those of certain individuals. Based on this he classified human bloods into three groups, namely group A, group B, and group C. He defined that group A blood agglutinates with group B, but never with its own type. Similarly, group B blood agglutinates with group A. Group C blood is different in that it agglutinates with both A and B. This was the discovery of blood groups for which Landsteiner was awarded the Nobel Prize in Physiology or Medicine in 1930. (C was later renamed to O after the German Ohne, meaning without, or zero, or null.) Another group (later named AB) was discovered a year later by Landsteiner's students Adriano Sturli and Alfred von Decastello without designating the name (simply referring it to as "no particular type"). Thus, after Landsteiner, three blood types were initially recognised, namely A, B, and C.

Czech serologist Jan Janský was the first to recognise and designate four blood types in 1907 that he published in a local journal, using the Roman numerical I, II, III, and IV (corresponding to modern O, A, B, and AB respectively). Unknown to Janský, American physician William L. Moss introduced an almost identical classification in 1910, but with Moss's I and IV corresponding to Janský's IV and I. Thus the existence of two systems immediately created confusion and potential danger in medical practice. Moss's system was adopted in Britain, France, and the US, while Janský's was preferred in most other European countries and some parts of the US. It was reported that "The practically universal use of the Moss classification at that time was completely and purposely cast aside. Therefore in place of bringing order out of chaos, chaos was increased in the larger cities." To resolve the confusion, the American Association of Immunologists, the Society of American Bacteriologists, and the Association of Pathologists and Bacteriologists made a joint recommendation in 1921 that the Jansky classification be adopted based on priority. But it was not followed particularly where Moss's system had been used.

In 1927, Landsteiner, who had moved to the Rockefeller Institute for Medical Research in New York, and as a member of a committee of the National Research Council concerned with blood grouping suggested to substitute Janský's and Moss's systems with the letters O, A, B, and AB, first instroduced by Polish physician Ludwik Hirszfeld and German physician Emil von Dungern. There was another confusion on the use of O which was introduced in 1910. It was never clear whether it was meant for the figure 0, German null for zero or the upper case letter O for ohne, meaning without; Landsteiner chose the latter.

In 1928 the Permanent Commission on Biological Standardization adopted Landsteiner's proposal and stated:

The Commission learns with satisfaction that, on the initiative of the Health Organization of the League of Nations, the nomenclature proposed by von Dungern and Hirszfeld for the classification of blood groups has been generally accepted, and recommends that this nomenclature shall be adopted for international use as follows: 0 A B AB. To facilitate the change from the nomenclature hitherto employed the following is suggested:

This classification became widely accepted and after the early 1950s it was universally followed.

Hirszfeld and Dungern discovered the inheritance of blood types as Mendelian genetics in 1910 and the existence of sub-types of A in 1911. In 1927, Landsteiner, with Philip Levine, discovered the MN blood group system, and the P system. Development of the Coombs test in 1945, the advent of transfusion medicine, and the understanding of ABO hemolytic disease of the newborn led to discovery of more blood groups. As of December 2023, the International Society of Blood Transfusion (ISBT) recognizes 45 blood groups.