Bombay Blood Group: HH & OH Negative Genetic Basis & Transfusion Challenges

Updated on September 23, 2026Author:NEXT IAS Contributors

The Bombay Blood Group, also known as the hh or oh negative phenotype, is one of the rarest blood groups in the human biological system. This blood group was discovered in the city of Mumbai, formerly known as Bombay, in 1952, and it defies the traditional ABO blood grouping system because of the absence of the H antigen on the red blood cells.

In case of a blood transfusion, people with this blood type can receive blood only from other H deficient donors. 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.

Problem with Blood Transfusion

S.No.	Problem	Brief description
1	Allergic reaction	It can cause the recipient with the problem of itching and rash due to sensitivity to proteins in donor blood.
2	Fever	It may cause fever, chills or shivering due to an immune reaction to the donor.
3	Transfusion reaction	A serious reaction caused primarily by incompatible blood such as ABO mismatch. The immune system destroys the red cells which are being transfused. It can cause fever, back or chest pain, dark color urine, shock and kidney injury.
4	Transfusion infection	Sometimes the blood can rarely transmit infections such as hepatitis B, hepatitis C, HIV, malaria or bacteria. Such risk is very low where the screening systems are very strong.
5	Bacterial contamination or Sepsis	The presence of bacteria in blood may cause high fever, low blood pressure and severe infection.
6	Transfusion-related acute Lung injury (TRALI)	It is a rare but serious immune problem that causes sudden breathing difficulty and fluid accumulation in the lungs usually within 6 hours.
7	Circulatory overload (TACO)	The frequent blood transfusion may overload the heart and circulation and can cause breathlessness and increased blood pressure. This problem is common in older adults and people with heart or kidney disease.
8	Excess of Iron	The frequent transfusions of blood or red cells can lead to excess deposition of iron in the liver, heart and endocrine organs which may lead to organ damage.
9	Electrolyte and metabolic problems	The blood transfusions in high amounts may disturb potassium, calcium and acid-base balance which can affect heart rhythm and other body functions.
10	Alloimmunisation	The recipient may develop antibodies against donor red-cell and can make future transfusions very difficult to match.

Historical Background of Bombay Blood Group

In Bombay, India, an individual was discovered to have an interesting blood type that reacted to other blood types in a way that had not been seen before.
Serum from this individual contained antibodies that reacted with all RBCs from normal ABO phenotypes (i.e., groups O, A, B, and AB).
The individual’s RBCs appeared to lack all of the ABO blood group antigens and an additional antigen that was previously unknown.
In 1952, a paper about the “new blood group character related to the ABO blood group” was published.
This new blood group character is the H antigen and it is the building block for the antigens of the ABO blood group.
It was named for the city in which it was first discovered, the ‘Bombay phenotype’ describes individuals whose RBCs lack the H antigen.
Because the A and B antigens cannot be formed without the H antigen precursor, their RBCs also lack these antigens.
As a result, these individuals produce anti-H, anti-A, and anti-B and can thus be transfused only with RBCs that also lack the H, A, and B antigens i.e., they can only receive blood from another person with the Bombay phenotype.
Because of the rarity of this blood type, this normally means using blood donations from a suitable relative.

List of Blood Group Compatibility

S. No.	Blood Group	Can Donate To	Can Receive From
1.	O-	O-, O+, A-, A+, B-, B+, AB-, AB+ (Universal Donor)	O-
2.	O+	O+, A+, B+, AB+	O-, O+
3.	A-	A-, A+, AB-, AB+	O-, A-
4.	A+	A+, AB+	O-, O+, A-, A+
5.	B-	B-, B+, AB-, AB+	O-, B-
6.	B+	B+, AB+	O-, O+, B-, B+
7.	AB-	AB-, AB+	O-, A-, B-, AB-
8.	AB+	AB+ only (Universal Recipient)	All types

Genetic Basis and Mechanism of the Bombay Blood Phenotype

The Bombay phenotype results from homozygous recessive inheritance of the h allele (hh genotype).
Normally, most people have at least one H allele, producing the H substance—a carbohydrate chain on red blood cell surfaces.
In Bombay individuals, the lack of H means no foundation for A or B sugars, so their cells appear “blank”.
However, their plasma forms with potent anti-H, anti-A, and anti-B antibodies, which agglutinate (clump) any non-Bombay blood introduced.
A related variant, the para-Bombay phenotype, retains some H antigen in secretions but not on cells, adding further complexity.

Prevalence Worldwide

Globally, the Bombay blood group affects about 0.0004% of people, or approximately 1 in 250,000 to 1 million.
In Mumbai, prevalence rises to about 1 in 10,000, linked to consanguineous marriages in western and southern India.
It is more common in India, Pakistan, Bangladesh, and some Middle Eastern pockets, though urbanization may dilute it through diverse gene pools.
Registries like those in Mumbai help track donors and are vital during medical emergencies.

Medical Challenges in Transfusions for HH & OH Negative Blood Group

Bombay patients can donate to any ABO group since their cells lack A, B, or H antigens, acting as “universal donors” in that sense—but they cannot receive from anyone else.
O blood transfusion causes severe hemolytic reactions, including fever, chills, hemoglobinuria (red urine), and life-threatening renal failure from anti-H antibodies reacting with the O cells' H antigen.
Misdiagnosis as O is common without H-specific testing, leading to serious complications.
Only Bombay-to-Bombay transfusions are safe.
Kidney or liver transplants from non-Bombay patients also pose a risk of antibody incompatibility.