what's the most common blood type
When discussing blood types, the two groupings most commonly used are the ABO (A, B, AB, O) and Rh (+, -) systems. The least common blood type in humans is Bombay (EXTREMELY rare), which is a type O with missing H antigen. Otherwise, of the normal ABO and Rh typings, the least common group is AB-. ABO from most to least frequent: O, A, B, AB. The relative frequencies of these groups varies depending on race.