Hh Antigen System - Problems With Blood Transfusion

Problems With Blood Transfusion

The first person that was discovered to have the Bombay Phenotype seemed to have an interesting blood type that reacted to other blood types in a way never seen before. The serum contained antibodies that reacted with all RBCs normal ABO phenotypes. The red blood cells appeared to lack all of the ABO blood group antigens plus an additional antigen that was previously unknown.

Individuals with the rare Bombay phenotype (hh) do not express H antigen (also called substance H), the antigen which is present in blood group O. As a result, they cannot make A antigen (also called substance A) or B antigen (substance B) on their red blood cells, whatever alleles they may have of the A and B blood-group genes, because A antigen and B antigen are made from H antigen; For this reason people who have Bombay phenotype can donate RBCs to any member of the ABO blood group system (unless some other blood factor gene, such as Rhesus, is incompatible), but they cannot receive any member of the ABO blood group system's blood (which always contains one or more of A and B and H antigens), but only from other people who have Bombay phenotype.

Receiving blood which contains an antigen which has never been in the patient's own blood causes an immune reaction due to the immune system of a hypothetical receiver producing immunoglobulins not only against antigen A and B, but also against H antigen. The most common immunoglobulins synthesized are IgM and IgG (and this seems to have a very important role on the low hemolytic disease of the newborn).

It's very important in order to avoid any complications during a blood transfusion to detect Bombay phenotype carriers because the usual tests for ABO blood group system would show them as group O. Since Anti-H immunoglobulins can activate the complement cascade, it will lead to the lysis of RBCs while they are still in the circulation, provoking an acute hemolytic transfusion reaction. This, of course, cannot be prevented unless the lab technologist that is involved has the means and the thought to test for Bombay group.