Discovery of the ABO Blood Groups

Before 1901, surgeons who attempted blood transfusion had no way to predict whether the procedure would save a patient or kill one. Some recipients tolerated infusions from healthy donors without incident; others developed hemolytic crises within minutes and died. The failures were blamed on technique or on the patient's constitution. Landois had shown in 1875 that animal blood cells clump in human vessels, but no one had compared blood between people.

Karl Landsteiner changed that with an economical experiment. Working as an assistant in the Department of Pathological Anatomy at the University of Vienna, he collected serum and red cells from himself and five colleagues, then mixed every possible pairing in small tubes and recorded which produced visible agglutination. The results fell into three reproducible groups, which he labeled A, B, and C in his November 1901 paper in the Wiener klinische Wochenschrift. The C group was later renamed O to reflect its lack of A or B antigens. In 1902 Alfred von Decastello and his student Adriano Sturli identified the fourth group, AB, whose cells carry both antigens and whose serum carries neither antibody.

The immunological explanation followed directly from the data. A person's serum contains antibodies against whatever antigens are absent from their own cells: type A individuals carry anti-B, type B carry anti-A, and type O carry both. Transfusing the wrong group introduced foreign antigens into a host primed to destroy them. Landsteiner had described a two-part antigen and antibody system. Because the groups are inherited, he suggested by 1903 that they could help settle disputed paternity.

Clinical adoption took time. World War I created a large demand for transfusion, but many military surgeons paid little attention to blood grouping or compatibility tests. Grouping became practical once Moss showed that blood could be typed in two to five minutes with standard sera, and in 1921 Percy Lane Oliver founded a volunteer donor service in London under the British Red Cross. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930; in 1927 he and Philip Levine had described the MN and P blood group systems.

Compatibility testing for red cell transfusion still rests on the system Landsteiner found in the blood of himself and five colleagues. Crossing sera against cells kept finding new groups: in 1940, at the Rockefeller Institute in New York, Landsteiner and Alexander Wiener described the Rh factor.