Explain Rh Blood Grouping System

Some individuals also have a so called Rh antigen on the surface of their RBCs. Those who have it are called Rh (+) and those who do not have it are Rh (-). This is the basis of the Rh blood group system. In Caucasian (white) races, about 85% of human are Rh +ve, but among African blacks almost everyone is Rh -ve.

Rh stands for Rhesus monkey. RBC of Rhesus monkey when injected into rabbit develops antibodies to rhesus RBC. Later, it was discovered that rabbit serum containing anti- rhesus antibodies could agglutinate not only rhesus RBC, but also human RBC in about 85% cases, which was suggestive that these 85 % of human beings have on their RBC an antigen identical to or remarkably similar to Rhesus RBC. This antigen was named as 'Rh antigen'. Human beings having this antigen were labeled 'Rh positive'. Thus, in a Rh system, blood may be either positive or negative. A person with Rh -ve blood does not have Rh antibodies naturally in the blood plasma (as one can have A or B antibodies, for instance).

But a person with Rh -ve blood can develop Rh antibodies in the blood plasma if he or she receives blood from a person with Rh+ve blood, whose Rh antigens can trigger the production of Rh antibodies. A person with Rh+ve blood can receive blood from a person with Rh -ve blood without any problems. So it must be clear by now that Rh positive or negative individuals do not have anti Rh antibodies. But, ifan Rh -ve individual is given Rh +ve blood, he develops anti Rh-ve antibodies. Rh incompatibility can therefore occur sometime.