Most of us grow up thinking there are only eight blood types. You’ve got your A, B, AB, and O, each with a plus or a minus attached like a grade on a middle school spelling test. If you're O-negative, you’re the "universal donor" everyone wants at the blood drive. If you're AB-positive, you're the "universal recipient" who can take a pint from just about anybody. But honestly, that’s just the surface level. It's the tip of a very deep, very complex iceberg. When you start asking what type blood is rarest, the answer isn't just a letter; it’s a story about genetic mutations that sound like something out of a sci-fi novel.
The world of hematology is messy. We’ve identified over 45 different blood group systems containing hundreds of unique antigens. Most people never need to know this. You go through life just fine without knowing if you're positive for the Kell antigen or the Duffy system. But for a tiny fraction of the population—people with what we call "Golden Blood"—knowing their type is a matter of life and death.
The Real Answer: RH-Null is the Rarest of the Rare
If we are talking about absolute numbers, the title for what type blood is rarest goes to Rh-null. It is so rare that researchers estimate only about 50 people on the entire planet have it. Since it was first discovered in an Indigenous Australian woman in 1961, doctors have only confirmed around 43 to 50 cases worldwide.
Why is it called "Golden Blood"? It isn't actually gold-colored, obviously. It’s "golden" because it is a universal donor for anyone with a rare blood type within the Rh system. If you lack all 61 possible antigens in the Rh system, your body will violently reject almost any other blood. But Rh-null has none of those antigens. It is a blank slate. To a hematologist, a bag of Rh-null is more valuable than its weight in 24-karat gold because it can save the life of someone whom no other blood can help.
But there is a catch. A big one. If you have Rh-null, you can only receive Rh-null blood. Because your body isn't used to any Rh antigens, it views even the most common "O-negative" blood as a foreign invader. Imagine being one of 50 people on Earth and knowing that if you need a transfusion, your donor might be living three continents away. It’s a terrifying reality. People with this type are often encouraged to bank their own blood throughout their lives just in case of an emergency.
Breaking Down the Common "Rares"
Most people aren't looking for the "1 in 6 billion" answer when they search for what type blood is rarest. They want to know where they sit in the standard ABO system. In that context, AB-negative is the rarest of the common types.
In the United States, only about 0.6% of the population has AB-negative blood. That’s roughly 1 in every 167 people. It’s rare, sure, but you likely know someone who has it or have stood next to them in line at the grocery store.
✨ Don't miss: High Protein in a Blood Test: What Most People Get Wrong
Here is how the percentages usually shake out in a general population (though this shifts wildly depending on your ethnic background):
O-positive is the heavyweight champ. About 37% to 38% of people have it. It’s the most common type across almost every demographic. O-negative follows at around 7%, which is why the Red Cross is always calling those donors—they are the emergency room heroes.
Then you get into the "B" types. B-positive sits around 8.5%, while B-negative is a mere 1.5%.
AB-positive is about 3.4%.
And then there's AB-negative. The "unicorn" of the standard system. 0.6%.
Geography Changes the Game
If you're in Central Asia, B-positive isn't rare at all; it’s actually quite common. In certain parts of India, the "rare" B types are found much more frequently than in Western Europe. Genetics is local.
🔗 Read more: How to take out IUD: What your doctor might not tell you about the process
There is also the "Bombay Phenotype" (h/h blood group). It was first discovered in Mumbai (then Bombay) in 1952 by Dr. Y.M. Bhende. This type is fascinating because it tests as Type O, but it’s actually missing the "H" antigen that even Type O blood usually has. If you have Bombay blood and you get a transfusion of standard O-positive or O-negative blood, you’ll have a severe reaction. In India, it occurs in about 1 in 10,000 people. In Europe? It’s 1 in a million.
Why Does This Even Matter?
You might think this is just medical trivia. It isn’t. Knowing what type blood is rarest helps hospitals manage their inventories and helps donors understand their "power."
If you have a rare type, your donation isn't just a nice gesture. It is a lifeline that literally cannot be replaced by anything else. Synthetic blood doesn't exist yet—at least not in a way that works for humans. We are still entirely dependent on the kindness of strangers and the needles of phlebotomists.
The International Society of Blood Transfusion (ISBT) recognizes 45 blood group systems. Some of these are incredibly specific to certain ethnic groups. For instance, the "U-negative" type is found almost exclusively in individuals of African descent. If a patient with U-negative blood needs a transfusion, a donor pool of 10,000 Caucasian donors might not yield a single match. This is why diversity in blood donation is just as important as the volume of blood collected.
The Mystery of Antigens and Evolution
Evolutionary biologists still argue about why we have different blood types at all. Some evidence suggests that certain blood types offered protection against specific diseases. For example, Type O might provide a slight survival advantage against severe malaria. Others suggest that the "A" and "B" antigens appeared as mutations that helped our ancestors survive different plagues.
We are living records of our ancestors' survival. Your blood type is a 5-million-year-old history book.
💡 You might also like: How Much Sugar Are in Apples: What Most People Get Wrong
When you look at the Rh system—the plus or minus—it gets even weirder. The Rh factor is named after the Rhesus macaque, though we now know human Rh factors are different from those in monkeys. If a mother is Rh-negative and her baby is Rh-positive, her body might actually treat the baby as a foreign object. We have medicine for that now (RhoGAM), but for most of human history, this was a silent, mysterious killer of newborns.
What You Should Do Next
If you don't know your blood type, find out. Seriously.
You don't need a fancy DNA kit. The easiest way to find out is to go donate blood. They will test it for free and mail you a card with your type on it. It’s the most productive "diagnostic test" you’ll ever take because you’re helping someone else while getting your own data.
If you find out you have a rare type—especially something like O-negative, B-negative, or AB-negative—make a plan.
- Register with a rare donor database. Organizations like the American Rare Donor Program (ARDP) keep track of people with "difficult" blood to ensure they can find each other in a crisis.
- Carry a medical ID. If you have a type like Rh-null or Bombay Phenotype, you need to wear a bracelet. In an unconscious emergency, a standard "O-neg" transfusion could kill you.
- Bank your own blood. If you have an upcoming surgery and a rare type, talk to your doctor about "autologous donation." You give blood to yourself a few weeks before the procedure.
Understanding what type blood is rarest isn't just about winning a pub quiz. It’s about understanding the fragile, incredible biology that keeps us alive. Whether you are the most common O-positive or the one-in-a-million Rh-null, your blood is the most sophisticated liquid on the planet. Don't take it for granted.
Check your medical records or schedule a donation today. It’s the only way to know if you’re carrying "gold" in your veins.