- Rh factor
- An antigen found in the red blood cells of most people: those who have Rh factor are said to be Rh positive (Rh+), while those who do not are Rh negative (Rh-) Blood used in transfusions much match donors for Rh status as well as for ABO blood group, as Rh- patients will develop anemia if given R+ blood. Rh typing is also important during abortion, miscarriage, pregnancy, and birth, as mother and fetus may not be Rh-compatible. Rh stands for rhesus monkeys, in whose blood this antigen was first found. See also RhoGAM, Rh incompatibility.
* * *Rh factor 'är-'āch- n a genetically determined protein on the red blood cells of some people that is one of the substances used to classify human blood as to compatibility for transfusion and that when present in a fetus but not in the mother causes a serious immunogenic reaction in which the mother produces antibodies that cross the placenta and attack the red blood cells of the fetus called also rhesus factor
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* * *Rhesus factor any of numerous antigens (agglutinogens) that may be present on the membrane of erythrocytes and that determine the Rh blood group system; the most common ones are called (in one system) Rh 1, Rh 3, Rh 4, Rh 5, and Rh 21. See Rh blood group, under blood group. Called also Rh antigen.
Medical dictionary. 2011.