Different blood types are prevalent in different parts of the world. In the United States, AB-negative is the rarest blood type, while O-positive is the most common.
Your blood type is based on genetics and whether it contains certain antigens. While AB/Rh-negative may be the rarest blood type in the United States, this is not the case worldwide.
Keep reading to learn more about blood types and why it’s hard to say which type is the rarest in the world. You’ll also learn why it’s important to know your blood type and how you can obtain this information.
Every drop of blood contains red blood cells, which carry oxygen throughout your body. It also contains white blood cells, which help fight infection, and platelets, which help your blood clot.
But that’s not where it ends. Your blood also contains antigens, which are proteins and sugars that sit on red blood cells and give blood its type. Though there are at least 33 blood typing systems, only two are widely used. These are the ABO and the Rh-positive/Rh-negative blood group systems.
ABO system
Two of these important antigens have been labeled A and B. You can have either or both antigens on your blood cells, as determined by your genetics. If neither of these antigens is present, the blood is type O.
Rh factor
Blood is also typed according to the Rh factor. This is another antigen found on red blood cells. If the cells have the antigen, they’re considered Rh-positive. If they don’t have it, they’re considered Rh-negative.
Depending on whether the Rh antigen is present, each blood type is assigned a positive or negative symbol.
Together, these two groups form the eight basic blood types that most people are familiar with:
| A-positive | B-positive | AB-positive | O-positive |
| A-negative | B-negative | AB-negative | O-negative |
It’s hard to say which blood type is the rarest in the world because they’re linked to genetics. That means the prevalence of certain blood types varies widely in different parts of the world.
But in the United States, AB-negative is considered the rarest blood type, and O-positive is the most common. The Stanford School of Medicine Blood Center ranks blood types in the United States from rarest to most common as follows:
| Blood type | Average percent of U.S. population |
| AB-negative | .6% |
| B-negative | 1.5% |
| AB-positive | 3.4% |
| A-negative | 6.3% |
| O-negative | 6.6% |
| B-positive | 8.5% |
| A-positive | 35.7% |
| O-positive | 37.4% |
Again, this ranking isn’t universal. In India, for example, the most common blood type is B-positive, while in Denmark, it’s A-positive.
These variations also exist within groups of Americans. According to the Red Cross, Asian Americans are much more likely to have a B-positive blood type than Latin Americans and white Americans, for instance.
Rhnull or “golden blood”
Rhnull is a rare blood type that doesn’t contain any Rh-antigens in red blood cells. Also nicknamed “golden blood” due to its extreme rarity, only
As scientists continue to learn more about Rhnull phenotypes, it’s important to let your doctor know you have this type of blood if you ever need a transfusion. Due to the scarcity of golden blood, there’s a small group of regular donors worldwide.
People with Rhnull blood phenotypes may also be at risk of developing chronic hemolytic anemia, which causes your body to destroy immature red blood cells.
Blood types are determined by genetics. Like many traits, you inherit one gene from each of your parents to create a pair.
You might inherit an A gene from one parent and a B gene from the other, resulting in the AB blood type. You could also get B antigens from both parents, giving you a BB, or a B, blood type.
On the other hand, type O doesn’t contain any antigens and doesn’t affect A and B blood types. This means that if you inherit an O from one parent and an A from the other, your blood type would be A.
It’s also possible that two people with type A or type B blood could have a baby with type O blood if they carry the recessive O gene.
Six of these combinations (AA, AB, BB, AO, BO, OO) are called genotypes. The four blood types (A, B, AB, and O) stem from these genotypes.
| Parent #1 | AB | AB | AB | AB | B | A | A | O | O | O |
| Parent #2 | AB | B | A | O | B | B | A | B | A | O |
| Child’s possible blood type | A, B, or AB | A, B, or AB | A, B, or AB | A or B | O or B | O, A, B, or AB | O or A | O or B | O or A | O |
Your immune system naturally contains protective substances called antibodies. These help fight off foreign bodies your immune system doesn’t recognize. Usually, they attack viruses and bacteria. But antibodies can also attack antigens that aren’t in your natural blood type.
For example, if you have type B blood mixed with type A blood during a transfusion, your antibodies will destroy blood cells with the A antigens. This can have life threatening results, which is why medical centers worldwide have strict procedures to keep this from happening.
To add complexity, blood types don’t always need to be an exact match to be compatible. For example, AB blood has both the A and B antigens, so a person with this type of blood can receive either type A or B blood.
Everyone can receive type O blood because it doesn’t contain any antigens. This is why people with type O blood are considered “universal donors.” But people with type O blood can receive only type O blood.
When it comes to the Rh factor, people with Rh-positive blood can receive either Rh-positive or Rh-negative blood, while people with Rh-negative blood can receive only Rh-negative blood.
In some cases, a person with Rh-negative blood can carry a child with Rh-positive blood, resulting in a dangerous condition called Rh incompatibility.
The best way to learn what blood type you have is by giving a blood sample. You can ask your healthcare professional to check for your blood type during regular blood testing, or you may find out this information when donating blood. There are even at-home test kits you can purchase.
It’s not uncommon to not know your blood type. But this key piece of information can be important to know in case of an emergency, like the need for a blood transfusion.
While everyone’s blood generally looks the same, a complex set of systems is used to categorize what goes on beneath the surface. There are dozens of blood typing systems, but the most used are the ABO and Rh systems, which provide the eight basic blood types.
Generally, AB-negative is considered to be the rarest blood type. But because blood type is linked to genetics, there’s no single type considered the rarest worldwide.