(Hemoglobin hh,  H blood group)

Extremely rare, most common in people of Indian origin (Reunion Island). Incidence: 1/10.000 in India.

Autosomal recessive transmission of a mutation of gene FUT-1 (long arm of chromosome 13). This mutation causes an inactivation of fucosyl-transferase, and therefore an inability to produce the H carbohydrate on the surface of which red blood cells antigens A and B get hooked.

Conventional blood tests show that the patient is Group O while he is carrying  anti-A, anti-B and anti-H (O) antibodies: a transfusion with O blood entails a major risk of hemolytic reaction !

The FUT-2 gene, also located on the long arm of chromosome 13, codes for a fucosyl-transferase that is expressed in bodily secretions, especially saliva.

Patients with inactive FUT-1 and FUT-2 genes present the full Bombay phenotype.

Patients whose FUT-1 gene only is inactive are called para-Bombay because the presence of the H antigen in their secretions (and therefore at the same time A or B or AB antigen) entails they carry only anti-H antibodies: they cannot be transfused with group O blood !

Anesthetic implications:

to be suspected in at-risk populations; those patients must only be transfused with hh blood (very rare,frozen). Consider predonation or normovolemic hemodilution.

References :

-        Deo N, Odejinmi F, Dawlatly B, Khan A.
Bombay blood group and pregnancy: a rare clinical scenario.
J Obstet Gynaecol 2005, 25:398-9

-        Chatterjee P, Alagumalai K, Panneerselvam S.
Role of acute normovolemic hemodilution in pregnancy for emergency cesarean section in a patient with Bombay blood group.
Cureus 2023 ; 15(4): e37995. doi:10.7759/cureus.37995

Updated: April 2023