The Bombay Blood Group is rare blood group with absence or deficiency of H Antigen . Bombay blood phenotype was first discovered in Bombay in India by Dr. Y.M. Bhende in 1952. Named for the city in which it was first discovered. It is a blood group which shows absence of A, B, H antigens on red cells and presence of anti-A, anti-B and anti-H antibodies in serum. The H antigen is located on the surface of red blood cells and is the precursor of A and B antigens. H antigen can be synthesized by H gene FUT1 and FUT2 which is located on chromosome 19 and give rise to glycosyl transferase that add 1-fucose to a precursor substance to produce H antigen on red cells. Bombay group would be categorized as O group because they wouldn’t show any reaction to anti-A and anti-B antibodies just like a normal O group. When a cross matching is done then it would show cross-reactivity or incompatibility. The reverser or serum grouping has to be performed to detect the Bombay blood group.
THE ‘H’ ANTIGEN
Karl Landsteiner in his discovery of the famous ABO blood types identified that the red blood cells have an “H” antigen on their cell surfaces. This H antigen is the precursor of A & B antigens. This H antigen is modified into “A” or “B” antigen like wise and the individual get either “A” ,”B” or “AB” blood group. This modification occurs in the presence of a Transferase Enzyme. If this enzyme is lacking, then the “H “antigen is not modified and these individuals have the “O” blood group.
Detection of Bombay Phenotype
This blood group may be commonly mistaken as ‘O’ and many a time, not identified at all if proper blood grouping or testing practices are not followed. During routine grouping conducted at the hospital’s blood bank, the blood group may show up as O, with no reaction to Anti-A and Anti-B antibodies. However, Bombay Phenotype is detected when reverse grouping is performed; it shows agglutination with O cells, proving the rare Bombay ‘Oh’ Phenotype blood. It is important to be cautious in predicting the ABO blood type of children based on the phenotypes of their parents. This is due to the fact that a third antigen (H) on the surface of red cells can prevent the expected ABO blood type from occurring. Repeated testing is then done as it is important to perform reverse grouping or serum grouping to detect the Bombay Blood group.
Individuals with Bombay blood group can donate to all ABO blood group people and can only accept from Bombay blood group people. The Bombay anti-H is an IgM antibody that can bind complement and cause red cell lysis. Because the H antigen is common to all ABO blood group, Bombay blood is incompatible with all ABO donors.
PROPERTIES OF BOMBAY BLOOD GROUP
1. Absence of H, A and B antigens; NO agglutination with anti-A, anti-B, or anti-H lectin.
2. Presence of anti-A, anti-B, anti-AB and potent wide thermal range anti-H in the serum.
3. A, B, H non-secretor (no A, B, or H substances present in saliva).
4. Absence of H enzyme in serum and H antigen on red cells.
5. Presence of A or B enzymes in serum and red cells.
6. A recessive mode of inheritance.
7. Red cells of the Bombay group are compatible only with the serum from another Bombay individual.
Author is Retd. Prof. of Pathology, NMCH Patna , Prof. of Pathology ,VIMS Pawapuri, Nalanda Bihar, Prof. of Pathology: PDM University, B.Garh, Prof. of Pathology SIMS Anwarpur, Hapur, UP