Rhesus blood group system
The Rhesus (Rh) blood group system is next in importance to the ABO system in blood transfusion practice but it is not of equal significance in every country because the frequency of the most important of the Rhesus antigens, i.e. D antigen, varies in
different populations as follows:
Examples. Rhesus (D) positive
Asian. 90–98%
African 94–95%
Nepalese 99–100%
Oriental. 99–100%
South American people: 91- 97%
Ecuador, Chile, Brazil,
Argentina, Uruguay: 82–94%
Caucasian About 85%
Rhesus antigens
The Rhesus blood group system consists of six genes: Cc, Dd, Ee. A single chromosome can carry C but not c, D but not d, and E but not e. A person inherits from each parent a set of three closely positioned Rhesus genes, e.g. CDe/cde. At least 36 Rhesus genotypes are possible based on the combinations of genes that can be inherited ).
When using the Fisher-Race derived nomenclature, Rhesus antigens bear the same name as their genes, i.e. antigens D, C, c, E and e (d gene is not expressed).
Rhesus antigens are only expressed on
red cells. They are not found in body fluids.
Medically, antigen D is the most important of the Rhesus antigens because it is the most immunogenic, capable of producing immune (IgG) anti-D antibody which can cause haemolytic reactions. A person is grouped as Rhesus (Rh) positive or negative based on the presence or absence of antigen D:
- Rh positive: A person inherits gene D and their red cells express antigen D.
- Rh negative: A person does not inherit gene D and their red cells do not express antigen D.
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