The rarest blood in the world is Rh-null, sometimes called “golden blood.” Only about 43 people have ever been reported to have it. Rh-null red blood cells are missing all of the more than 50 antigens in the Rh blood group system, making this type so scarce that a global coordination network exists just to track the handful of known carriers.
But rarity depends on how you define it. If you’re asking about the standard blood types most people encounter, AB negative is the rarest at roughly 1 in 100 people. Beyond that familiar system, several exotic blood types are vanishingly uncommon and create serious challenges when someone who carries one needs a transfusion.
Rh-Null: Golden Blood
Your red blood cells carry surface markers called antigens, and the Rh system alone contains more than 50 of them. Most people have heard of one: the “positive” or “negative” label (Rh D) tacked onto your ABO type. Rh-null blood lacks every single Rh antigen, not just Rh D but all the others too. That complete absence is what earned it the nickname “golden blood,” both for its extreme rarity and for its theoretical value in transfusion medicine.
Because Rh-null cells carry no Rh antigens, they won’t trigger an immune reaction based on Rh mismatches in a recipient. That makes golden blood compatible with a wide range of Rh types, which sounds like a medical miracle until you consider the other side of the equation: people with Rh-null blood can only safely receive Rh-null blood themselves. With roughly 43 known cases worldwide, finding a compatible donor in an emergency is extraordinarily difficult. Carriers often bank their own blood in advance of any planned surgery.
The Bombay Phenotype
Another contender for rarest blood is the Bombay phenotype, sometimes written as Oh. Standard ABO blood typing relies on a foundation molecule called the H antigen. The A and B antigens are built on top of it. In people with the Bombay phenotype, a mutation in the gene responsible for producing the H antigen means it never forms on red blood cells. Without that scaffold, A and B antigens can’t attach either. The result is blood that looks like type O on a basic test but is fundamentally different.
This distinction matters in a life-or-death way. If someone with the Bombay phenotype receives ordinary type O blood, their immune system will attack the transfused cells because those cells carry the H antigen that Bombay blood lacks entirely. Only blood from another Bombay-type donor is safe.
The prevalence varies dramatically by geography. In parts of Mumbai, roughly 1 in 10,000 people carry it. Across Europe, the rate drops to about 1 in 1,000,000. That geographic clustering is why it was first identified in Bombay (now Mumbai) in 1952 and why blood banks in India are far more likely to maintain a small reserve of Bombay-type units than those in Western countries.
Kell-Null and McLeod Phenotype
The Kell blood group system is another set of antigens on red blood cells, separate from both ABO and Rh. People with the Kell-null (K0) phenotype lack all Kell antigens. This occurs in about 0.001% of most populations, with slightly higher rates in Finland and Japan. Unlike Rh-null, Kell-null red blood cells function normally. The problem surfaces only during transfusion: once exposed to Kell antigens from donated blood, a Kell-null person can develop antibodies that make future transfusions dangerous. They need Kell-null blood going forward.
A related condition called McLeod syndrome takes things further. It’s caused by a mutation on the X chromosome that disrupts a protein needed to properly display Kell antigens on red blood cells. Because it’s X-linked, it primarily affects males. Beyond transfusion complications, McLeod syndrome causes progressive neuromuscular problems, including involuntary movements, muscle wasting, and sometimes heart disease. It’s one of the few rare blood phenotypes that carries health consequences beyond the blood bank.
AB Negative: The Rarest Common Type
Within the everyday ABO system that most people encounter during a blood draw or on a donor card, AB negative is the least common. About 1% of blood donors carry it. For comparison, O positive is the most common type at around 37% of the U.S. population, and O negative (the well-known universal donor for red cells) makes up about 7%.
Blood type distribution also shifts across ethnic groups. Roughly 45% of white Americans are type O, compared to 51% of Black Americans and 57% of Hispanic Americans. These population-level differences mean that a type considered uncommon in one community may be slightly more or less available in another, which affects local blood bank supplies.
What Makes a Blood Type Officially “Rare”
The International Society of Blood Transfusion defines a rare blood type as one where the person is missing a high-prevalence antigen found in fewer than 1 in 1,000 donors, or where someone lacks a combination of common antigens that rarely occurs together. By that standard, dozens of blood types qualify as rare, not just the headline-grabbing ones. The challenge is that many of these types aren’t detected by routine blood typing. They only come to light when a patient has an unexpected transfusion reaction or when advanced antibody screening picks up something unusual.
To manage this, a global network called the International Rare Donor Panel has operated since 1965 under a joint initiative of the World Health Organization and the ISBT. Maintained by a reference laboratory in Bristol, UK, the panel currently holds records of rare donors from 27 countries along with inventories of frozen rare blood units stored in blood banks worldwide. When a hospital identifies a patient with an exceptionally rare type, the panel can locate a compatible unit across international borders, sometimes shipping frozen blood thousands of miles.
Why Rarity Creates Real Risk
For someone with a common blood type, a needed transfusion is straightforward. For carriers of rare types, every medical situation involving potential blood loss carries extra weight. Planned surgeries require weeks of advance coordination. Unexpected trauma is the worst-case scenario, because there may simply be no compatible blood available locally or even nationally.
Carriers of golden blood, the Bombay phenotype, or Kell-null often donate blood for themselves (a process called autologous donation) and store frozen units. Some also donate for the broader rare blood supply, knowing their contribution could be the only match for another carrier somewhere in the world. In communities where the Bombay phenotype is more common, dedicated registries and donor drives help maintain a small but critical reserve.
The rarity of these blood types also makes genetic counseling relevant for families. Many rare phenotypes are inherited in a recessive pattern, meaning both parents must carry the gene variant. In populations where a specific rare type clusters, couples may want to know whether their children could inherit a blood type that complicates future medical care.