The Rarest Blood Types in the WorldIncluding Rhnull and Bombay Phenotype - 2026
When people ask "what is the rarest blood type," most mean the rarest of the 8 common ABO/Rh types: that is AB-negative at 0.6% of US donors. But outside the 8-type system, blood types exist that are vanishingly rare - some with only a handful of known cases worldwide.
AB-Negative: Rarest of the 8 Major Types
Among the 8 blood types defined by ABO and Rh systems, AB-negative is the rarest. Only approximately 0.6% of US blood donors are AB-negative. That equates to roughly 6 in every 1,000 donors. In a room of 200 people, you would expect just one or two to be AB-negative.
AB-negative is rare because both conditions must simultaneously be true: the person must carry both A and B antigens (which already restricts to the AB group at roughly 4-5% of the population), and they must be Rh-negative (roughly 15% of people). The joint probability of both is very low.
AB-negative individuals are critically valuable plasma donors because AB plasma is universally compatible. Blood banks specifically seek AB-negative (and AB-positive) plasma donors.
Full AB-Negative guide +Rhnull: Golden Blood (Approximately 50 Known Cases Worldwide)
Rhnull blood lacks all Rh antigens. The Rh blood group system consists of over 50 antigens - Rhnull people have none of them. This is not just lacking the common Rh-D antigen (which defines Rh-negative), but lacking all Rh antigens completely.
Rhnull is sometimes called "golden blood" because of its extraordinary rarity and medical usefulness - in theory, Rhnull red cells could be given to anyone with rare Rh antibodies. As of published literature, approximately 40-50 people worldwide have been identified with Rhnull blood, though the true number may be slightly higher given that many people are never typed in detail.
The challenge for Rhnull individuals is severe: they can only receive blood transfusions from other Rhnull donors. Any standard blood transfusion - even O-negative - carries Rh antigens that Rhnull people would react against. In an emergency, Rhnull individuals face extreme transfusion risk. Several known Rhnull donors have made advance arrangements to store their own blood (autologous donation) for anticipated surgeries.
Rhnull arises from mutations in the RHAG or RHCE/RHD genes. There are two genetic types: regulator type (mutations in RHAG) and amorph type (mutations in RHD/RHCE). It is inherited recessively, meaning both copies of the relevant gene must be mutated.
Bombay Phenotype (h/h): Cannot Receive Standard O Blood
The Bombay phenotype (also called the Oh blood group or hh phenotype) is caused by mutations in the FUT1 gene, which prevents the production of the H antigen. The H antigen is a biochemical precursor to both A and B antigens. Without H antigen, A and B antigens cannot form at all - and critically, Bombay phenotype people produce anti-H antibodies.
Here is the clinically dangerous implication: standard O-negative blood carries H antigen. An O-negative transfusion given to a Bombay phenotype patient would trigger their anti-H antibodies, causing a severe haemolytic reaction. Even O-negative - the universal donor for standard ABO/Rh typing - is incompatible with Bombay phenotype patients.
The only compatible blood for Bombay phenotype patients is from other Bombay phenotype donors - which is a vanishingly small pool. Bombay phenotype affects approximately 1 in 10,000 people in certain parts of India (particularly Maharashtra state) and is extremely rare elsewhere (1 in 1,000,000 in Europe). Global prevalence is estimated at less than 0.001%.
Standard blood typing in ABO/Rh systems misidentifies Bombay phenotype as group O because the serological test looks for A and B antigens (absent in Bombay) but may not test for H antigen. This is why all Bombay phenotype patients should carry a medical alert card and inform their care team.
Duffy-Negative: Common in African Populations
The Duffy blood group system consists of antigens on the Duffy antigen receptor for chemokines (DARC protein). Being Duffy-negative (lacking Fya and Fyb antigens, the Fy(a-b-) phenotype) is not rare overall - it is found in approximately 68% of African Americans and up to 99% of people from West Africa.
Duffy-negative has a clinically fascinating implication: the Duffy antigen is the receptor that Plasmodium vivax malaria parasites use to enter red blood cells. People without the Duffy antigen have near-complete resistance to P. vivax malaria. This is believed to explain why Duffy-negative is so prevalent in sub-Saharan Africa, where P. vivax malaria has historically been endemic.
Duffy-negative individuals who receive Duffy-positive blood may develop Duffy antibodies after transfusion. These antibodies are clinically relevant in subsequent transfusions and in pregnancy (Duffy antibodies can cause mild haemolytic disease of the newborn). For patients with sickle cell disease who require frequent transfusions, Duffy-matched blood is preferred to prevent sensitisation.
Other Notable Rare Types: Kell, MNS, Kidd
Beyond ABO, Rh, Duffy, and Bombay, there are approximately 40 officially recognised blood group systems and hundreds of antigens. Most are clinically irrelevant for routine transfusion, but several matter in specific patient populations:
Kell-null (K0)
Lacks all Kell antigens. Very rare. Kell antibodies are clinically significant and can cause severe HDN. K-antigen is relevant in young women who may become pregnant.
McLeod phenotype
Lacks all Kx and Kell antigens. Associated with McLeod neuroacanthocytosis syndrome (a neurological condition). Extremely rare - fewer than 100 known cases worldwide.
Jk(a-b-) Kidd-null
Lacks all Kidd antigens. Kidd antibodies are notoriously transient - they may disappear and reappear, making them clinically dangerous because they may be missed on a pre-transfusion antibody screen.
MNS rare variants
The MNS system includes antigens relevant in transfusion for sickle cell patients needing closely matched blood. En(a-) and U-negative phenotypes are rarer variants requiring matched units.
What Having a Rare Blood Type Means for You
If you know you have a rare blood type, several practical steps can significantly improve your safety:
- Carry a medical alert card with your exact blood type including rare antigens
- Register with a rare donor program - the American Rare Donor Program (ARDP) connects rare donors with patients who need matched units
- Discuss autologous donation (banking your own blood before elective surgery) with your surgeon
- Ensure your family members are typed - they may share your rare phenotype and be compatible donors
- If you have known antibodies, carry a current antibody identification card from your transfusion medicine service