Rh factor or Rh antigen is a type of surface protein present on the surface of RBCs. It forms the basis of the Rh blood grouping system. Both the ABO blood grouping and Rh blood grouping are based on the presence or absence of different surface proteins or antigens on RBCs.
Rh antigen is present in around 80 percent of humans. Individuals with Rh antigens are referred to as Rh +ve and those without Rh antigens are referred to as Rh -ve. The positive or negative sign next to the different blood groups denotes the Rh factor. E.g. ​​A+, B-, O-, and AB+, etc.
The Rh antigen is similar to the antigen present in Rhesus monkeys, therefore it is named ‘Rh’ antigen. The Rh blood grouping was given by Karl Landsteiner and A.S. Weiner. There are many Rh antigens identified. The Rh D is the most common Rh antigen and causes the most severe immune reaction.
It is important to match the Rh group also, along with the ABO groups before transfusion. If a person with Rh-negative blood is given Rh-positive blood, then the body starts making antibodies against the Rh antigen. Therefore a Rh -ve person should only be given Rh -ve blood.
Erythroblastosis foetalis
This is a haemolytic condition that occurs due to the incompatible blood types of a mother and her foetus. This condition arises when the mother is Rh-negative and the foetus is Rh-positive. In the first pregnancy, the blood of Rh -ve mother and Rh +ve foetus does not mix due to the placental barrier. But during delivery, there are chances that some of the Rh +ve foetal blood enters the maternal bloodstream. If the maternal blood (Rh -ve) gets exposed to the Rh +ve blood of the foetus, the mother starts producing antibodies against the Rh antigen. In the case of second or subsequent pregnancies with Rh +ve foetus, there are chances that the Rh antibodies in the maternal blood mixes with the foetus blood. In that case, the Rh antibodies from the maternal blood will destroy the RBCs of Rh +ve foetus. This can result in severe anaemia, jaundice and even lead to the death of the foetus, or an infant after birth.
To prevent this, the mother is given anti-Rh antibodies after delivery that neutralises any Rh +ve fetal blood cells entering the maternal bloodstream, before the mother’s immune system can develop antibodies.
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