The rarest blood type in the world is Rh-null, sometimes called “golden blood.” Fewer than 50 people on Earth are known to have it, and fewer than 10 active donors exist worldwide. But “rarest” depends on how you define it. Within the familiar A-B-O system most people know, AB negative is the rarest, found in only about 0.6% of the U.S. population. Beyond both of those, there are extremely rare regional blood types that most people have never heard of.
Rh-Null: The World’s Rarest Blood Type
Rh-null blood lacks every single antigen in the Rh blood group system. Most people carry dozens of these Rh proteins on the surface of their red blood cells. Rh-null individuals carry none. This makes their blood extraordinarily rare and, in theory, universally compatible for donation to anyone within the Rh system, which is why it earned the nickname “golden blood.”
The condition is genetic. It results from mutations in a gene on chromosome 6 called RHAG, which is responsible for assembling Rh proteins on red blood cells. When both copies of this gene are altered, the cell surface ends up completely bare of Rh antigens. Because it requires inheriting the mutation from both parents, Rh-null tends to appear in families with a history of marriages between close relatives.
Living with Rh-null blood creates a serious medical dilemma. The very thing that makes it valuable for donation makes it dangerous for the person who has it. If you have Rh-null blood and need a transfusion, the only truly safe option is blood from another Rh-null donor. Even O negative blood, typically considered the universal donor type, still carries Rh antigens that an Rh-null recipient’s immune system could attack. A mismatched transfusion can trigger reactions ranging from fever and jaundice to kidney failure.
With fewer than 10 known donors scattered across the globe, finding compatible blood in an emergency is nearly impossible. People with Rh-null blood are often advised to bank their own blood ahead of any planned surgery and to manage conditions like anemia aggressively with iron and folic acid to reduce the chance of ever needing a transfusion.
AB Negative: Rarest in the ABO System
If you’re thinking about the standard blood types you see on donor cards, AB negative is the rarest. Only about 0.6% of the U.S. population has it. That means roughly 1 in every 167 people. AB negative individuals carry both A and B antigens on their red blood cells and lack the Rh D antigen (the “positive” or “negative” part of your blood type).
Despite being rare as a donor type, AB negative people have a modest advantage as recipients: they can generally receive red blood cells from any negative blood type (A negative, B negative, O negative). The practical challenge is on the donation side. Because AB negative blood is so uncommon, blood banks often have limited supply, and people with this type are strongly encouraged to donate regularly.
The Bombay Phenotype: Rare and Easy to Mistype
One of the most medically significant rare blood types is the Bombay phenotype, first discovered in Mumbai (then Bombay) in 1952. People with this blood type lack a foundational molecule called the H antigen, which serves as the building block for A and B antigens. Without it, their red blood cells can’t display A, B, or even O antigens in the normal way. On standard blood tests, Bombay phenotype blood looks like type O, but it is not. Giving these individuals regular type O blood can trigger a life-threatening transfusion reaction.
The Bombay phenotype occurs in about 1 in 10,000 people in India, with slightly higher rates in southern states like Tamil Nadu and Karnataka. In Europe, it drops to roughly 1 in 1,000,000. The condition is recessive, meaning you need to inherit the gene variant from both parents, and it appears more frequently in populations where marriages between relatives are common. One study from Andhra Pradesh found a notably higher prevalence in communities with a history of consanguineous marriage.
Blood Types That Vary by Ancestry
Some blood group variants are rare overall but extremely common in specific populations. The Duffy-null phenotype is a striking example. Among people of European or Asian descent, fewer than 1% have it. But among people of African ancestry, the frequency is 80 to 100%. Roughly two out of three Black Americans carry the Duffy-null phenotype. This isn’t a disorder. It’s an inherited trait that likely became widespread because it offered some protection against certain types of malaria parasites, which use the Duffy protein as a doorway into red blood cells.
Duffy-null status has medical relevance beyond transfusions. It’s associated with lower baseline white blood cell counts, a finding called benign ethnic neutropenia. This can cause confusion in clinical settings when lab results flag a “low” white blood cell count that is actually normal for that individual.
Why There Are So Many Blood Types
Most people think of blood type as a simple label: A, B, AB, or O, positive or negative. In reality, the International Society of Blood Transfusion recognizes 48 distinct blood group systems. Each system is defined by different proteins or sugars on the surface of red blood cells, and each one can carry multiple antigen variants. The familiar ABO system is one. The Rh system, which includes the D antigen that determines “positive” or “negative,” is another, and it alone contains over 50 recognized antigens.
This complexity means that the concept of a “perfect match” goes far deeper than the basic eight blood types. For most routine transfusions, matching ABO and Rh D is sufficient. But for patients who need frequent transfusions, such as those with sickle cell disease or certain cancers, even minor antigen mismatches can cause the immune system to build antibodies against donor blood over time. That’s when the rarer blood group systems start to matter, and when finding a compatible donor can become genuinely difficult.
What Makes a Blood Type “Rare”
Blood banks generally classify a blood type as rare when fewer than 1 in 1,000 donors carry it. By that standard, dozens of blood types qualify. The American Rare Donor Program maintains a registry of people with unusual antigen profiles so hospitals can locate compatible blood when a patient’s type doesn’t match anything on the shelf.
For most people, your blood type will never cause a medical problem. If you don’t know your type, a simple blood draw can identify it, and donating blood is the easiest way to find out. If you do happen to have a rare type, knowing about it ahead of time gives you and your medical team a significant head start if you ever need surgery or emergency care.