Two doctors once used the same numbers for opposite blood types
In 1907 the Czech serologist Jan Janský labelled blood groups I to IV. Unaware of him, the American physician William L. Moss used the same numerals, but his group I was Janský's IV and vice versa. Britain, France and the US followed Moss while most of Europe used Janský, a dangerous muddle for transfusions.
It all began in Vienna. In 1900 Karl Landsteiner noticed that red blood cells clumped when mixed with serum from certain other people, the first sign that human blood was not all alike. The next year he sorted blood into groups he called A, B and C, identifying two surface markers and two matching antibodies, work that earned him the 1930 Nobel Prize in Physiology or Medicine. His students Adriano Sturli and Alfred von Decastello found a fourth type in 1902 but left it unnamed.
In 1910 Ludwik Hirszfeld and Emil von Dungern renamed C as 0, for null, called the fourth type AB, and first explained how the groups are inherited. Even after a 1921 joint recommendation by American professional societies to adopt Janský's scheme on grounds of priority, places using Moss's numbering ignored it. Resolution came from Landsteiner himself, who by 1927 was at the Rockefeller Institute in New York and proposed plain letters O, A, B and AB, choosing O as in ohne, German for without. This new Landsteiner classification was used everywhere by the early 1950s.
Reuben Ottenberg first applied blood typing to transfusion in 1907, and large-scale use took off in the First World War once citric acid was used to stop clotting. Felix Bernstein worked out the correct inheritance pattern in 1924. A single gene controls the type through three alleles; A and B are both dominant over O and codominant with each other, so type O requires two O copies.
ABO remains the most important of 48 blood group systems recognised by the International Society of Blood Transfusion, and it also occurs in apes and monkeys. Type O mutations seem to have arisen at least three separate times in human history.
Source: ABO blood group system
