Lab technician places labeled blood samples in refrigerator for safe preservation.
Most people know their blood type as one of eight possibilities: A+, A–, B+, B–, AB+, AB–, O+, O–. These are the ABO and Rh-D designations — the ones that matter most for routine transfusion.
But human blood is far more complex. Red blood cells carry over 350 known blood group antigens organised into 45 blood group systems. Beyond ABO and Rh-D, dozens of other antigen systems — Kell, Kidd, Duffy, Lewis, MNS, Diego, and many more — can cause immune reactions in patients who receive blood lacking an antigen they have developed antibodies against.
For the vast majority of patients, these additional antigens are irrelevant. For a small but important minority — patients with chronic transfusion dependence (thalassemia, sickle cell disease), patients with rare inherited blood conditions, and patients who have developed antibodies from multiple previous transfusions — they are critical. And for the rarest cases, finding compatible blood is so difficult that a patient may wait days or weeks, their life depending on a donor in a registry somewhere in India who matches their unique antigenic profile.
A blood type is considered rare when fewer than 1 in 1,000 people lack a high-frequency antigen (one present in the vast majority of the population) — or when a person has a combination of uncommon antigen negativities that makes finding compatible blood exceptionally difficult.
In practice, Indian blood banking recognises several categories of rare blood situations:
1. Rare ABO phenotypes — like the Bombay blood group, discussed in detail below
2. Rh-negative in antigen-rich sub-systems — patients with extended Rh negativity across multiple sub-antigens (not just Rh-D) who need extended-matched blood
3. Kell-negative blood — approximately 9% of people are Kell-negative; for the roughly 9% of people with Kell antibodies, only Kell-negative blood is safe
4. Multi-alloimmunised patients — patients with thalassemia or sickle cell disease who have received many transfusions and developed antibodies against multiple blood group antigens; they may need blood negative for 3, 4, or more rare antigens simultaneously
The Bombay blood group (also written as hh phenotype or Oh blood group) was first discovered in Mumbai (then Bombay) in 1952 by Dr. Y.M. Bhende. It is found almost exclusively in South Asia — approximately 1 in 10,000 people in India — versus roughly 1 in 1,000,000 in Europe and North America.
Normal blood types (A, B, AB, O) all share a common building block antigen on their red blood cells called H antigen. The A and B antigens are modified versions of H. Even type O blood has abundant H antigen.
People with the Bombay phenotype have a rare genetic mutation that prevents them from producing H antigen entirely. Their red blood cells carry no H antigen — and therefore no A or B antigen either, since A and B are built on H.
This creates a paradox that explains why Bombay blood is so dangerous to transfuse incorrectly:
This makes the Bombay blood group one of the most medically precarious situations in all of transfusion medicine. A Bombay patient requiring emergency surgery or experiencing massive haemorrhage cannot receive blood from any standard blood bank inventory, regardless of type.
India's estimated Bombay prevalence of 1 in 10,000 translates to approximately 140,000–170,000 people with Bombay blood — the largest Bombay population in the world by far.
India has an unofficial Bombay blood group registry with approximately 350 registered Bombay donors — of whom perhaps 30 are immediately contactable and available at any given time. Against 140,000+ Bombay individuals who may someday need a transfusion, 30 active donors represents an almost impossibly thin margin of safety.
When a Bombay patient needs blood urgently, the blood bank typically:
Digital platforms like TheBloodApp are critical for exactly this scenario — the ability to instantly alert all registered Bombay donors across India is the fastest possible way to locate and mobilise a donor when minutes matter.
Recognising the critical need for rare blood donor tracking, India launched the Rare Blood Donor Registry of India (RDRI) — a national database of blood donors with rare blood types who have been identified through extended blood typing and are registered for contact in emergencies.
The RDRI, integrated with eRaktKosh infrastructure and gradually expanding its reach, provides:
As of recent data, India's RDRI has over 4,000 screened donors — a meaningful start, though far short of the full population of patients who will eventually need extended-matched blood.
Beyond the Bombay group, India's largest rare blood matching challenge involves patients with thalassemia major and sickle cell disease who have developed alloantibodies — immune antibodies against blood group antigens from previous transfusions.
Because thalassemia patients receive blood monthly from childhood, they are exposed to the antigenic profiles of many different donors. Even small differences in antigens like Kell, Kidd, Duffy, and Rh sub-antigens — antigens that are not routinely matched in most transfusions — can trigger immune responses over time.
A thalassemia patient who has developed anti-Kell and anti-Jk(a) antibodies (against Kidd system antigens) needs blood that is simultaneously:
In a blood bank that doesn't have extended typing data for its donors, finding this combination may require testing dozens of units. In a blood bank with a registered extended-matched donor pool — maintained through platforms like RDRI and communicated through apps like TheBloodApp — the search is dramatically faster.
If you have an unusual blood typing history — been told you have a rare type, had unusual reactions during previous transfusions, or been identified as lacking a high-frequency antigen — here is what to do:
Get extended typing done: At institutions like PGIMER Chandigarh, AIIMS Delhi, Christian Medical College Vellore, or major blood banks in Mumbai and Bengaluru, extended blood group typing beyond ABO and Rh-D is available. This determines your full antigenic profile.
Register with RDRI: If extended typing reveals a rare profile, ask to be registered in India's Rare Donor Registry.
Register on TheBloodApp with your blood type noted: Even without formal RDRI registration, indicating your ABO and Rh type on TheBloodApp ensures you are in a searchable donor network.
Consent to emergency contact: Make clear to blood bank staff that you consent to being contacted in emergencies — that your number can be shared when a patient urgently needs your rare type.
The Bombay phenotype is sometimes discovered incidentally — during routine blood typing that shows O type, followed by discrepant reactions. Some people discover they are Bombay when a family member needs blood and typing reveals unusual results.
If you:
— ask your blood bank about Bombay phenotype testing. It is a simple additional test. And if you are confirmed Bombay, your registration in the rare donor network may one day be the factor that saves another Bombay patient's life.
Register on TheBloodApp with your blood type. If you have a rare type, note it in your profile. India's 4,000+ RDRI registered rare donors are protecting hundreds of thousands of patients with rare blood needs. Every additional registration strengthens that protection. To find blood banks with extended typing capability near you, call the number listed in the app.
Sources: Wikipedia — Bombay Blood Group | PMC — Rare Blood Donor Registry India | NBTC India — Extended Matching | GoAid India — Blood Type Guide | Stanford Blood Center — Rare Blood Types | PMC — Alloimmunisation Thalassemia India | eRaktKosh MoHFW — Rare Blood Types
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