Blood Types Explained - A, B, AB and O - Red Cross Blood
https://www.redcrossblood.org/donate-blood/blood-types.html
WebThere are four major blood groups determined by the presence or absence of two antigens, A and B, on the surface of red blood cells. In addition to the A and B antigens, there is a protein called the Rh factor, which can be either present (+) or absent (–), creating the 8 most common blood types ( A+, A- , B+, B- , O+, O- , AB+, AB- ).
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