More than 100 years ago, Dr. Karl Landsteiner discovered that not all red blood cells are alike. He found that, when different people's blood was mixed, it would often clump up and curdle, destroying the cells within it. His work on the different types of red blood cells led to the discovery of the ABO blood group system, which won him the 1930 Nobel Prize in physiology or medicine and also helped make blood transfusion a safe, reliable practice that saves millions of lives every year.
Many people know where they fit into the classic ABO blood typing system, which designates blood as type A, B, AB or O. But these four basic blood groups aren't the end of the story.
