Bombay Blood Group (hh): Rarest Blood Type — Complete Guide

The Bombay Blood Group — technically known as the hh blood group or Bombay phenotype — is one of the rarest blood types in the world. Unlike the common ABO blood groups (A, B, AB, O), people with the Bombay blood group lack the H antigen that normally serves as the precursor for A and B antigens. This makes them appear as O blood type on simple ABO testing, but they cannot receive O blood (or any other ABO type) — they can only receive blood from other Bombay phenotype donors.

First discovered in Bombay (Mumbai) in 1952 by Dr. Y.M. Bhende, the Bombay blood group has since been found worldwide but remains extraordinarily rare: approximately 1 in 10,000 people in India and 1 in 1,000,000 in the rest of the world.

For UPSC, the Bombay Blood Group is a frequently tested Science & Technology topic — covering genetics, blood transfusion medicine, and India's contribution to medical science.

Discovery

1952 Discovery in Mumbai

The Bombay Blood Group was first identified on January 30, 1952 by:

• Dr. Y.M. Bhende (V.M. Bhende), a pathologist at K.E.M. Hospital, Mumbai
• Observed while conducting routine blood tests
• Found a patient whose blood did not match any known ABO type
• Initially appeared to be O group, but further testing revealed unique serological properties
• The patient had anti-A, anti-B, AND anti-H antibodies

Publication

The discovery was published in The Lancet (British medical journal) in 1952, with the co-authors:

• Dr. Y.M. Bhende
• Dr. C.K. Deshpande
• Dr. L.I. Bhatia

Why "Bombay"?

The blood group was named after the city where it was discovered — then called Bombay (now Mumbai). Despite the rename to Mumbai, the medical terminology "Bombay Blood Group" is retained globally.

Understanding the Bombay Phenotype

Normal ABO Blood System

In the ABO blood system:

1. H antigen is the precursor — present in everyone with ABO groups
2. A antigen forms by adding specific sugar to H antigen
3. B antigen forms by adding different specific sugar to H antigen
4. AB — both A and B antigens
5. O — only H antigen (no A, no B)

Bombay (hh) Phenotype

In Bombay individuals:

• H antigen is absent because the "H" gene is homozygous recessive (hh)
• Therefore, NO H antigen → NO base for A or B antigens
• Blood test shows "O-like" appearance (no A, no B agglutination)
• BUT the person has anti-H antibodies (reactive against any blood with H antigen)
• This means they cannot receive ANY standard ABO blood type — all regular blood has some H antigen

Genetics

Key genetic fact:

• H gene controls H antigen production
• Normal allele: H (dominant)
• Bombay allele: h (recessive)
• To have Bombay phenotype, person must have genotype hh (homozygous recessive)

Pedigree Implications

• If both parents are HH — all children normal
• If one parent HH, other Hh — ~50% Hh, 50% HH (all normal)
• If both parents Hh (carriers) — 25% hh (Bombay), 50% Hh (carriers), 25% HH
• Two Bombay parents (hh × hh) — all children Bombay

This explains why the Bombay blood group is more common in endogamous (intra-community marriage) populations — increases probability of inheriting two h alleles.

Frequency

Global Distribution

Bombay blood group frequency varies significantly by region:

Why Higher in India?

Multiple factors contribute to higher Indian frequency:

• Endogamy (same-community marriage) — maintains the recessive h allele in the population
• Caste/community boundaries — limited gene flow historically
• Founder effects — some communities have higher rates
• Consanguineous marriages (in some regions) — increase homozygosity

Identification and Testing

Why It's Often Missed

The Bombay blood group is frequently misidentified as O blood group because:

• Both show no A or B antigens on normal testing
• Standard blood group tests don't always check for H antigen
• The patient may have a lifetime of "O" blood group designation

Correct Identification

To correctly identify Bombay blood group:

1. Ulex europaeus seed extract test — contains anti-H lectin
2. Bombay blood does NOT react with Ulex europaeus (no H antigen)
3. Normal O blood strongly reacts
4. Serum crossmatch — Bombay serum contains anti-H antibody that agglutinates all other ABO types

Forward and Reverse Grouping

Forward typing (antibodies added to blood cells):

• Bombay: No reaction to anti-A, anti-B — appears O
• Normal O: No reaction to anti-A, anti-B (same)

Reverse typing (test sera against known red cells):

• Bombay: Strong agglutination with O cells (due to anti-H)
• Normal O: No agglutination with O cells

This reverse typing discrepancy is the key to identifying Bombay phenotype.

Medical Significance

Blood Transfusion

Critical issue: Bombay individuals can ONLY receive:

• Bombay blood group (hh) blood
• NOT O negative or any other "universal donor" blood
• Even O- blood will cause severe transfusion reaction

If given regular O- blood (mistakenly thinking it's compatible):

• Severe hemolytic transfusion reaction
• Life-threatening
• Kidney failure, shock, potential death

Pregnancy

Rh incompatibility ISSUES:

• Bombay women pregnant with non-Bombay (Hh or HH) child
• Anti-H antibodies cross the placenta
• Hemolytic disease of the newborn — severe

This is particularly challenging because:

• Parents must know the condition
• Specialized monitoring required
• Intrauterine blood transfusions sometimes necessary

Emergency Transfusion

The challenge of finding Bombay blood in emergencies:

• Only few blood banks maintain supplies
• Directed donation from known Bombay donors often needed
• Autologous blood storage recommended before planned surgeries
• Family members may be compatible donors (due to genetics)

Bombay Blood Donor Networks

Mumbai and India

Given its discovery location and relatively higher frequency in India, Mumbai has:

• Bombay Blood Group Society (Mumbai)
• Networks of registered Bombay blood donors
• Directed donation systems
• Emergency contact lists

Major Blood Banks with Bombay Blood

• K.E.M. Hospital, Mumbai (where the blood group was discovered)
• Tata Memorial Centre, Mumbai
• AIIMS, Delhi
• PGI, Chandigarh
• Regional blood centres

Rare Donor Registry

India maintains a Rare Donor Registry:

• Bombay phenotype donors
• Other rare blood types
• Coordinated response for emergencies
• Managed by the National Blood Transfusion Council and state blood banks

Notable Cases

Historical Cases

The discovery itself (1952 Mumbai patient) led to:

• Awareness of the phenotype
• Research programs globally
• Understanding of blood group genetics

Modern Cases

In recent years, several high-profile cases have raised awareness:

• Mumbai resident needing Bombay blood during surgery — emergency appeals go viral
• Social media campaigns to locate donors
• Several Bombay phenotype patients have become public advocates for awareness

Management

For Bombay Phenotype Individuals

Recommended practices:

1. Registry registration as a rare donor
2. Notify family members of the condition (others may be carriers)
3. Medical documentation — keep records; inform doctors
4. Emergency contacts — know where Bombay blood is available
5. Autologous donation before planned surgeries (store your own blood)
6. Family blood typing — family members may be compatible

For Doctors and Hospitals

Essential steps:

1. Always do reverse typing for unusual ABO presentations
2. Know regional rare blood supplies
3. Maintain autologous blood storage facilities
4. Report cases to national registry
5. Counsel patients about marriage and family planning if relevant

India's Contribution to Medical Science

The Bombay Blood Group represents one of India's notable contributions to medical science:

Historical Significance

• Discovered in India, by an Indian — Dr. Y.M. Bhende
• Published in a major international journal
• Named after an Indian city
• Still known globally as the "Bombay Blood Group"
• Gold standard for understanding H antigen biology

Ongoing Research

Indian medical institutions continue research on:

• Regional frequency mapping
• Genetic markers of the h allele
• Transfusion management protocols
• Pregnancy monitoring for Bombay women

UPSC Relevance

GS3 (Science & Technology): Indian contributions to medical science, blood transfusion medicine, genetics.

Key Prelims facts:

• Bombay Blood Group = hh phenotype
• Discovered: 1952, Mumbai
• Discovered by: Dr. Y.M. Bhende (K.E.M. Hospital, Mumbai)
• Published in: The Lancet
• Frequency in India: ~1 in 10,000
• Frequency worldwide: ~1 in 1,000,000
• Highest frequency: Réunion Island (~1 in 1,500)
• Key characteristic: Lacks H antigen (genotype hh)
• Often misidentified as: O blood type
• Key difference: Cannot receive O or any standard blood type
• Test: Ulex europaeus (anti-H lectin)
• India's Rare Donor Registry: Maintained by NBTC
• Higher in India due to: Endogamy, consanguineous marriages, founder effects
• Can only receive: Other Bombay (hh) blood
• Compatible donors within a Bombay family: Possible (other hh members)