Bombay blood type
A rare type that looks like O on a routine test, yet can only safely receive blood from other Bombay donors.
The missing foundation
A and B antigens aren’t built from scratch. Your cells first make the H antigen, then an A or B enzyme adds one extra sugar to it. Type O people have plenty of unmodified H.
People with the Bombay phenotype inherit two non-working copies of the FUT1 gene (genotype hh), so they make no H at all. With nothing to build on, no A or B antigen appears either, whatever ABO genes they carry. Their plasma contains anti-A, anti-B and anti-H.
Why it matters
- Transfusion: because ordinary O cells are rich in H, anti-H destroys them. Bombay patients need Bombay blood, so India maintains donor registries for it.
- Inheritance puzzles: a Bombay parent who carries a hidden A or B gene can pass it on, so a child may be type A or B even though the parent “typed as O”. It is one of the textbook exceptions in the parent–child blood type chart.
- Where it’s found: about 1 in 10,000 people in India, higher in parts of Maharashtra and Karnataka; roughly 1 in a million in Europe.
Another ultra-rare type is Rh-null, “golden blood”.
Frequently asked questions
What is the Bombay blood group?
A rare blood type (hh or Oh) in which red cells lack the H antigen, the base structure A and B antigens are built on. It was first described in Mumbai (then Bombay) in 1952.
How common is the Bombay blood group?
About 1 in 10,000 people in India and roughly 1 in a million in Europe.
Who can a Bombay blood group person receive from?
Only other Bombay-phenotype donors. They have anti-H antibodies that react with ordinary type O blood as well as A, B and AB.
Can the Bombay phenotype be mistaken for type O?
Yes. Routine forward typing shows no A or B antigen, which looks like O. It is picked up when the plasma reacts against O cells in reverse typing or cross-matching.