What does Rh blood type mean?
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Rh stands for Rhesus—after the rhesus macaque (Macaca mulatta), or the rhesus monkey (associated with the development of the Rh factor and serum)— and is one of the major blood group systems in humans. The Rh system classifies blood as Rh-positive or Rh-negative, based on the presence or absence of Rh antibodies found in the blood. Similar to the ABO blood type, when it comes to blood transfusions, the Rh often matters: People with Rh-positive blood can have a transfusion of Rh-negative blood without a problem, but people with Rh-negative blood will have a transfusion reaction if they receive Rh-positive blood.