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Blood types and transfusion
1901 (Landsteiner); blood banks 1937· Invention or discovery· Medicine & surgery
Well documentedSolid records, physical evidence or scientific consensus.
The discovery that human blood comes in groups that must be matched, which made transfusion safe and blood banks possible.
See it on the Technology & Medicine map →How it works
Early transfusions often killed patients because mismatched blood clumps. In 1901 Karl Landsteiner in Vienna mixed blood samples and found three groups, later named A, B and O; his colleagues found AB in 1902. Matching groups made transfusion safe. Adding sodium citrate, from 1914–15, kept stored blood from clotting. Bernard Fantus opened the first hospital 'blood bank' at Cook County Hospital, Chicago, in 1937. Landsteiner also co-discovered the Rh factor in 1940.
Why it mattered
Transfusion made surgery, trauma care, childbirth emergencies and cancer treatment far safer; blood services now collect over 100 million donations a year worldwide.
How we know
Landsteiner's 1901 paper and 1930 Nobel Prize; transfusion records from World War I onward; Fantus's 1937 report in the Journal of the American Medical Association on the Cook County blood bank.
Still unknown or debated
Why blood groups exist at all is not fully known; one idea is that they evolved partly as defenses against infections such as malaria.
Connections (3)
▸Harvey's discovery of blood circulation was the basis for Blood types and transfusionMostly agreed
The connection
Once Harvey showed in 1628 that blood circulates in a loop, putting blood into a vein made sense. In the 1660s Richard Lower transfused blood between dogs, and Jean-Baptiste Denys gave lamb's blood to people, but deaths soon led France to ban the practice. Transfusion became safe only after Landsteiner found blood types in 1901.
When and how
Oxford and London, 1665–67 (Richard Lower); Paris, June 1667 (Jean-Baptiste Denys); Vienna, 1901 (Karl Landsteiner).
How sure are we?
Lower's and Denys's experiments were reported in the Royal Society's Philosophical Transactions, and they took circulation as their starting premise.
Debates and open questions
Some of Denys's patients survived, probably because they received little blood; one patient's death led to a murder trial in which Denys was cleared and the patient's wife was suspected.
▸Blood types and transfusion made possible matching for Organ transplantsMostly agreed
The connection
Landsteiner's 1901 discovery of the A, B and O blood groups showed that the immune system attacks mismatched cells. Transplant teams match blood groups between donor and recipient, and later tissue types too. Blood banks and transfusion also let surgeons replace the heavy blood loss of long transplant operations.
When and how
Vienna, 1901 (Karl Landsteiner); Chicago's first hospital blood bank, 1937; Jean Dausset's discovery of tissue types in Paris, 1958.
How sure are we?
Transplant protocols require blood-group compatibility; Landsteiner (1930) and Dausset (1980) won Nobel Prizes, Dausset for work that underpins transplant matching.
Debates and open questions
Blood-group barriers can now sometimes be crossed with antibody-removing treatments; how far mismatched transplants can safely go is still being studied.
▸Blood types and transfusion was a route of infection for the HIV/AIDS pandemicWell documented
The connection
Transfusions, and blood products made from the pooled plasma of thousands of donors, carried HIV before anyone knew the virus existed. People with hemophilia, who rely on clotting factor made from pooled plasma, were hit especially hard: roughly half of those in the US were infected. A blood test from 1985 made screening possible.
When and how
The US, Europe and Japan, roughly 1978–1985; the CDC reported a likely transfusion-linked AIDS case, a baby in San Francisco, in December 1982.
How we know
Tracing of recipients and donors, later confirmed by testing stored samples; official inquiries in France, Canada (1997) and Britain (2024) documented the infections.
Debates and open questions
How quickly governments and companies should have acted is contested; inquiries in several countries found delays in screening donors and heat-treating clotting products.