Blood types: What are blood types and what do they mean? - explainer

Your blood type is determined by several factors and is important in helping you get a blood transfusion if necessary. Here is everything you need to know.

Test tubes, taken by a health care worker, with plasma and blood samples after a separation process in a centrifuge during a coronavirus vaccination study at the Research Centers of America, in Hollywood, Florida, US, September 24, 2020. (photo credit: REUTERS/MARCO BELLO)
Test tubes, taken by a health care worker, with plasma and blood samples after a separation process in a centrifuge during a coronavirus vaccination study at the Research Centers of America, in Hollywood, Florida, US, September 24, 2020.
(photo credit: REUTERS/MARCO BELLO)

Blood types are a way that doctors have learned to classify the different types of blood. 

These classifications into different blood types are very important in making sure you get a healthy blood transfusion if necessary - a decision that could very well spell the difference between life and death.

Which blood type you have is genetic, but is determined based on certain antibodies and other inherited antigenic factors on the red blood cells or the lack thereof.

But what are the different types of blood types? What is the rarest blood type? What other important medical knowledge can be factored in from this?

Here is everything you need to know.

Red blood cells (illustrative) (credit: Wikimedia Commons)Red blood cells (illustrative) (credit: Wikimedia Commons)
What are the different blood types?

The International Society of Blood Transfusion recognizes 43 different blood group systems, the most famous of which are the ABO system and the Rh system, which are often used together.

The ABO system determines blood type based on a combination of two different antibodies and two different antigens, whereas the Rh tests for something called the Rh factor and determines if you have an Rh positive blood type or an Rh negative blood type.

 Inheritance of blood types from the father(blue) and the mother(red). The child's resulting blood type is marked in black. (credit: DAVIDSON INSTITUTE OF SCIENCE EDUCATION) Inheritance of blood types from the father(blue) and the mother(red). The child's resulting blood type is marked in black. (credit: DAVIDSON INSTITUTE OF SCIENCE EDUCATION)

In other words, ABO gives the letter, Rh gives the plus (+) or minus (-).

Red blood cells that present molecules of a certain type are termed Type A blood cells, while red blood cells that present another type of molecule are termed type B blood cells. Red blood cells that display both types of molecules on their surface are termed type AB blood cells, while cells that do not display either molecule are termed type O blood cells.

The human immune system recognizes these molecules and, upon encountering a molecule different from the type regularly present in the body, treats it as a foreign element that should be attacked. For example, if a person with type O blood receives a type A blood donation, his body will recognize the molecules of type A blood as foreign, consider the donor red blood cells as invaders and attack them. That is why it is imperative to adjust the donor blood type to the recipient’s blood type.

How many blood types are there?

Based on the ABO system and Rh system, there are eight blood types.

  • A+
  • A-
  • B+
  • B-
  • AB+
  • AB-
  • O+
  • O-

These are based on the antigens on the red blood cell and the antibodies in the blood plasma. 

  • A blood types have B plasma antibodies but A red blood cell antigens
  • B blood types have A plasma antibodies and B red blood cell antigens
  • AB blood types have neither A nor B plasma antibodies but A and B red blood cell antigens
  • O blood types have both A and B plasma antibodies but neither A nor B red blood cell antigens

These are determined by genetics, too. 

What is the rarest blood type?

The rarest blood type is AB-, also known as AB negative. This blood type is only found in a very small percentage of the global population and in individual countries. 

In Israel, for instance, around just 1% of the population has AB- blood type.

Rare blood types are essentially present in under one in every thousand people. Their true rarity is determined by other factors, such as the many other blood type grouping systems, and factors in hundreds of other antigens. In other words, the rarety might be determined outside the ABO and Rh systems.

What is the most common blood type?

While this varies from country to country to a small extent, globally, O+ blood type (O-positive blood type) is the most common blood type.

It is so numerous that in several countries, over half of the population has O+. In Ecuador and Peru, it's a far more solid majority that has an O-positive blood type.

But there are some things to consider. For instance, blood types in the B group are often more common in the Middle East.

What is the best blood type?

That depends on who you ask. 

In some respects, the best blood type might actually be the rarest blood type, AB+. This is because AB+ blood type is known as a universal receiver. In other words, if you have AB- blood type and need a blood transfusion, you can get it from any other blood type.

But then there is another blood type to consider, the universal donor.

What blood type is the universal donor?

The O- blood type (O-negative blood type) is the universal donor blood type. Technically, this just means it has the lowest risk of causing complications during a blood transfusion.

This is especially important in cases where there is a shortage of available blood, which often happens around the world.

However, O- blood type is only universal for red blood cells. AB blood types are the universal donor for plasma.

Keep in mind that blood types don't necessarily restrict themselves to only receiving blood from other blood types. But doing it with the same blood type is often the safest bet.

Is there a blood type diet?

Technically there are diets that exist that tell you what you should be eating for your blood type. However, these are fad diets unsupported by any scientific evidence.

Does your blood type determine your personality?

No. This idea of blood types determining your personality, such as having an O-positive personality, is a myth

This belief is especially popular in Japan and South Korea, but it is nothing more than a myth, considered pseudoscience wholly unsupported by evidence.

Essentially, your blood type has about as much actual scientific impact on your personality as your astrological sign.

Is there a link between blood type and COVID-19?

Early in the pandemic, there were some studies that indicated certain blood types could either help protect against severe cases of COVID-19 or put one at higher risk.

However, this is not true and has been debunked by further studies.

What may be true, though, is that some blood types may raise one's risk. Specifically, there have been studies indicating that people with an O blood type may be less likely to rest positive for COVID-19 even with symptoms. However, people who have AB+ blood type (AB positive blood type) or B+ blood type (B positive blood type) may be more likely to test positive.

The accuracy of this is still unclear, and further research is needed. And given how recent the COVID-19 pandemic is, that will be difficult.

Blood Test (credit: WIKIMEDIA COMMONS/ALDEN CHADWICK)Blood Test (credit: WIKIMEDIA COMMONS/ALDEN CHADWICK)
How בשמ טםו find out your blood type?

Many people actually don't know their blood type. The best way to do this is through a doctor by asking them to check your blood type. Or, if you donate blood, your blood type is usually tested and you can check with them.

There are also some at-home blood testing kits that are available.

Can your blood type change?

While your blood type is normally set in stone, that isn't always the case. In fact, there are a few ways your blood type can change - but it isn't usually for good reason.

The most common way your blood type can change is through a bone marrow transplant - and if you had to get one, it likely wasn't for anything good, like treating Leukemia.

Certain infections and cancers can also cause a change in blood type. However, the change is not always permanent.

However, changing a blood type can in some cases be a good thing. For example, recently, researchers at the University of Cambridge were able to change the blood type of a human kidney in order to make sure it can be used in a kidney transplant with someone with an incompatible blood type.

This is an exciting new accomplishment in the field of blood transfusion study and illustrates just how important blood types and our study of them are.