Rh system is the most commonly used blood group system after the ABO system. Within this system, there are 50 blood group antigens, though we commonly use the Rh factor (which refers to only one antigen- D antigen). Based on Rh factor, we define blood groups as Rh positive (contains D antigen) and Rh negative (does not contain D antigen). The presence or absence of this antigen affects the blood donation or receiving. A person with Rh negative blood can receive blood only from a donor with Rh negative blood. In comparison, a person with Rh positive blood can receive it from donors containing either Rh positive or Rh negative blood. In other words, a person with Rh negative blood can donate to anyone with either Rh positive or Rh negative blood, while donor with Rh positive blood can only donate to someone with Rh positive blood.
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