1. Karl Landsteiner discovered blood types in 1901 by observing that blood from people of different types would clot when mixed together. He later classified them as A, B and O.
2. ABO isn’t the only blood grouping system, however. There are currently 33 systems recognized by the International Society of Blood Transfusion, with monikers like Lutheran, Duffy, Hh/Bombay and Ok.
3. Blood type refers to different molecules on the surface of red blood cells. A mismatch of these molecules between donor and recipient can trigger a fatal immune reaction after a blood transfusion, as the recipient’s body attacks the outsider blood.
4. But not all blood types matter for all transfusions. Some variants are very rare, or exist only in certain ethnic groups, so the danger of getting a mismatch is, for most people, low.
5. The Junior blood type was formally classified just two years ago when researchers ...
