The Hh blood group

The Hh blood group contains one antigen, the H antigen, which is found on virtually all RBCs and is the building block for the production of the antigens within the ABO blood group.

H antigen deficiency is known as the "Bombay phenotype" (h/h, also known as Oh) and is found in 1 of 10,000 individuals in India and 1 in a million people in Europe. There is no ill effect with being H deficient, but if a blood transfusion is ever needed, people with this blood type can receive blood only from other donors who are also H deficient. (A transfusion of "normal" group O blood can trigger a severe transfusion reaction.)

Because the H antigen is the precursor of the ABO blood group antigens, if it is not produced, the ABO blood group antigens are also not produced. This can be misleading in paternity cases, a fact that has been exploited in soap opera story lines!

In the show "General Hospital", the father of Monica's child was in doubt. Monica had blood type A (genotype AO) and her child had blood type O (genotype OO). Because the child must inherit an O allele from the father, the father could have the genotype AO, BO, or OO. In other words, the child's father could have blood group A or B or O, which rules out Monica's husband Alan (type AB) and implicates Rick (type O).


1. How common is the Bombay Blood group in India?

1 of 10,000 Indians are found to have Bombay Blood Group.

2. Does Bombay blood group only affect Indians?

Bombay blood group is also seen in individuals besides Indians, though it is much rarer, amounting to one in a million cases in Europe.

3. What happens when a Bombay Blood group individual receives blood transfusion from an ABO blood group?

The patient is at a high risk of suffering from acute hemolytic transfusion reaction.