You’ve probably sat in a doctor's office or a high school biology class and heard that AB negative is the "unicorn" of the blood world. It makes sense. Only about 1% of people have it. It’s rare. It’s elusive. But honestly? AB negative is practically common compared to the real outlier.
There is a blood type so rare that only about 50 people on the entire planet are known to have it.
They call it Rh-null, or more dramatically, "Golden Blood." It isn’t actually gold, obviously. It looks like the same red stuff in everyone else. But to a doctor or a hematologist, it’s worth more than its weight in 24-karat bullion. If you're asking what's the most rarest blood type, Rh-null is the undisputed heavyweight champion. It was first discovered in 1961 in an Indigenous Australian woman, and it completely blew the minds of the medical community. Before her, doctors assumed that if you lacked all Rh antigens, you wouldn't even make it out of the womb.
Why Golden Blood Is the Absolute Rarest
Most of us think of blood in terms of A, B, and O. Then we slap a plus or a minus on it. That "plus" or "minus" refers to the Rh (Rhesus) system, specifically the D antigen. But the Rh system is actually a massive family of 61 different antigens.
Most people are missing a few.
But people with Rh-null? They’re missing all of them. Every single one.
Because they lack these proteins, their red blood cells aren't quite the same shape as yours or mine. They’re a bit fragile. This can lead to a type of mild chronic anemia, but the real danger isn't the health of the blood itself—it's the logistics of staying alive.
If you have Rh-null blood, you can only receive Rh-null blood.
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Think about that for a second. There are roughly 8 billion people on Earth. If you need a transfusion and you're one of the 50, you better hope one of the other 49 is nearby and feeling generous. Or, more likely, you've spent your life "banking" your own blood in a freezer just in case you ever trip on a sidewalk.
The Standard "Rares" (AB Negative and Friends)
Now, for most of us living in the real world of standard medical charts, what's the most rarest blood type usually points to AB negative. In the United States, about 0.6% of the population has it.
It’s a weird one.
- AB+ is the "universal recipient" (they can take anything).
- O- is the "universal donor" (they can give to anyone).
- AB- is a bit of a lonely middle ground.
If you have AB-, you can only receive from other negative types (O-, A-, B-, AB-). It’s the rarest of the "common" eight. If you walk into a Red Cross today, they’ll probably be happy to see you, but they won't exactly call the local news. If you walk in with Rh-null? They might lock the doors so you can't leave.
The Mystery of the Bombay Phenotype
There’s another contender in the "impossibly rare" category called the Bombay Phenotype (h/h).
Discovered in 1952 in Mumbai (then Bombay) by Dr. Y.M. Bhende, this one is a total curveball. Basically, these people lack the "H" antigen, which is the precursor to A and B.
Imagine you’re building a house. The H antigen is the foundation. A and B antigens are the paint colors. If you don't have the foundation, you can't have the paint. To a standard blood test, these people look like Type O. But if you give them Type O blood, their body treats it like a foreign invader and attacks.
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It’s found in about 1 in 10,000 people in India and about 1 in a million in Europe. It’s not quite "Golden Blood" rare, but it’s definitely "carry a medical alert bracelet at all times" rare.
Genetics: Why This Happens
Blood types aren't just random. They're a legacy. You get one half from your mom and one half from your dad.
The reason what's the most rarest blood type stays rare is because the genes required to produce things like Rh-null or Bombay are "autosomal recessive." This is a fancy way of saying both parents have to carry the specific, rare mutation and pass it on simultaneously.
It often pops up in communities where people don't move around much.
In the case of Rh-null, it’s so rare because it requires a complete "silencing" of the Rh genes. It’s a genetic glitch that happened once in a blue moon and survived.
The Ethics of Having Rare Blood
If you have Rh-null or another ultra-rare type, you’re in a weird spot. You are a universal donor for almost anyone with rare Rh-system blood. Your blood is a literal lifesaver. Scientists use it to develop treatments for things like Rhesus disease in babies.
But it’s a burden.
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Donors with Rh-null are often asked to fly across borders or donate on short notice to save someone they've never met. Because there are fewer than 10 active donors worldwide who actually give blood, the pressure is immense.
It’s a paradox. Your blood can save the world, but the world might not have any blood to save you.
How to Find Out If You're a "Unicorn"
Most people never actually learn their full blood profile. A standard test only checks for ABO and the D antigen.
If you want to know if you're part of the 1% (or the 0.000001%), you usually have to go deeper.
- Donate Blood: Most donation centers will tell you your basic type for free.
- Request a Phenotype Test: If you have a history of reactions to transfusions, doctors might do an "extended typing."
- Check Your Heritage: Certain rare types are tied to specific ethnicities (like U-negative being more common in people of African descent).
Honestly, most of us will just be O+ or A+. And that’s fine. It’s better than fine—it’s safe. Being "common" in the blood world means the hospital always has a bag of something on the shelf with your name on it.
If you’re curious about your own status, the best next step is to book a donation appointment at a local clinic. Not only will you find out your basic type, but you'll also be helping clear out the constant shortage that hospitals face. If it turns out you have something rare, the lab will definitely let you know—they'll be your new best friends.