Rh Factor: Are you positive or negative?


Ever pondered upon the + or – sign ahead of your blood type?
Rh blood types were discovered in 1940 by Karl Landsteiner and Alexander Wiener.  This was 40 years after Landsteiner had discovered the ABO blood groups. The Rh system was named after rhesus monkeys, since they were initially used in the research to make the antiserum for typing blood samples. 
Rhesus protein is second in its clinical importance only to the ABO blood group. The D antigen, discovered in 1939, was the first Rhesus antigen to be described. D positive patients were termed Rhesus-positive. In 1946, a quantitative variant with a weakly expressed D antigen was discovered and termed “Du”. This variant, now called “weak D”, is of clinical and diagnostic importance.
Since 1953, is has been clear that there are also qualitative variants of the D antigen. Although patients with this partial D variant are positive for the D antigen, they can also form anti-D. Up to 1% of all pregnant women have clinically significant anti-erythrocyte antibodies. 
Are you positive for Rh?

Rh factor is a protein embedded in the membrane of red blood corpuscles. Possessing this protein on the surface of RBC renders a positive phenotype and lack of the same makes you negative. This can be detected simply by a test for blood type and Rh status.
Rh Inheritance



Rh can be inherited from either of the parents, father or mother, independent of blood type ABO alleles. It is transferred from the parents to progeny through genes. There are two categories of Rh alleles, Rh positive and Rh negative, former being the dominant. An individual positive for Rh may have both alleles as Rh+/Rh+ or a copy of both Rh positive and Rh negative Rh+/Rh-.
Rh factor and Pregnancy
Medically, the Rh factor and blood types can create serious clinical complications. Commonest of all is mother-foetus incompatibility which occurs when wither the mother is Rh (-) and foetus is Rh (+). Maternal antibodies can cross the placenta and destroy the foetal red blood cells. Risk increases with each birth. Rh type mother-foetus incompatibility occurs only when an Rh+ man fathers a child with an Rh- mother.  Since an Rh+ father can have either a DD or Dd genotype, there are 2 mating combinations possible with differing risks as shown below.  Regardless of the father's genotype, if he is Rh+ and the mother is Rh-, doctors assume that there will be an incompatibility problem and act accordingly.

If the blood of an Rh-positive foetus gets into the bloodstream of an Rh-negative woman, her body will understand it is not her blood and will fight it by making anti-Rh antibodies. These antibodies can cross the placenta and try to destroy the foetus’s blood. This reaction can lead to serious health problems and even death in a foetus or new born.





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