Each person's
blood is one of four major types: A, B, AB, or O.
Blood types are determined by the types of antigens on the
blood cells. ... The
Rh factor is a
type of protein on the surface of red
blood cells. Most people who have the
Rh factor are
Rh-positive. Those who do not have the
Rh factor are
Rh-
negative.
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