Now researchers at the University of British Columbia have identified a new, more powerful group of enzymes that can turn any type of blood into the universally usable type O—expanding the pool of potential blood donors and making blood matching safer and easier.

"Blood type is determined by the presence of antigens on the surface of red blood cells; type A blood has the A antigen, B has the B antigen, AB blood has both antigens and O blood has none," said lead researcher Stephen Withers, a professor of chemistry at UBC. "Antigens can trigger an immune response if they are foreign to the body, so transfusion patients should receive either their own blood type, or type O to avoid a reaction. That's why O blood is so important."