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The Difference Between A, B, AB, and O Blood Types

Cartoon bags of blood with different types listed on them

Someone needs blood or platelets every 2 seconds in the United States, and nearly 16 million blood components are transfused each year. A car accident victim can require 100 units of blood, and one donation can save 3 lives. The importance of blood donation is obvious. But before you can donate blood, you should know your blood group. The most common method of classifying human blood is the ABO blood group system. Please continue reading to learn more about the four major blood groups and what they mean for blood transfusions.

Why is the blood group system important?

Matching blood types is necessary for a safe blood transfusion. Receiving a transfusion of the wrong blood type can be life-threatening. 

Each person’s blood type is determined by genes inherited from their parents. There are four main blood types in the ABO blood groups systemA, B, AB, and O based on what blood group antigens are present on the surface of the red blood cells. Each blood group can also either be Rhesus D (RhD) positive or RhD negative. So, there are eight main blood types: A negative, A positive, B negative, B positive, AB negative, AB positive, O negative, and O positive. 

What makes one blood type different from another?

To understand the difference between the blood groups, we need to understand antibodies and antigens. Human blood is made up of four main components - red blood cells, white blood cells, platelets, and a liquid called plasma. Antigens are protein molecules found on the surface of red blood cells. They activate or stimulate the body’s immune response. Antibodies are protein molecules found in the plasma and play a significant role in the body’s natural defense system. For example, they recognize foreign substances and alert the immune system about their presence. Your blood type depends on the type of antigens and antibodies present in your blood.

What is the difference between the blood groups?

Your blood type depends on two antigens (the A or B antigens) present on the red blood cells and the anti-A or anti-B antibodies present in the plasma. 

  • Blood type A has only the A antigen on the red blood cells and anti-B antibodies in the plasma.
  • Blood type B has only the B antigen on the red blood cells and anti-A antibodies in the plasma. 
  • Blood group AB has both A and B antigens on the red blood cells and neither anti-A nor anti-B antibodies in the plasma.  
  • Blood group O has no antigens on the red blood cells and both anti-A and anti-B antibodies in the plasma.

In addition to this, there is an Rh antigen or Rh factor. If this antigen is present on the red blood cells, the blood type is positive, and if it is absent, the blood type is negative.

In addition to the 8 common blood types, there is also something called a “rare blood type.” Besides the A and B antigens, there are more than 600 other antigens on red cells. You have a rare blood type if you don’t have specific antigens that 99% of people have. If you lack an antigen that 99.99% have, your blood type is labeled extremely rare. 

What is considered the best blood type?

People with O negative blood are universal red cell donors, meaning they can donate blood to a person with any blood type. The blood group O negative is the safest to give to someone whose blood type is unknown, for example, in a life-threatening emergency. It can also be used when there is a limited supply of the exact matching blood group. This is because the red cells don't have A or B antigens and don’t have the Rh antigen either. However, only about 7% of the population in the U.S. is O negative. 

Type O (both positive and negative) is in high demand and routinely in short supply at hospitals. This is because O positive is the most common blood group (37% of the population). The need for O negative is highest because it is the universal donor blood used for emergency transfusions.

It is worth noting that while universal red cell donors are people with type O negative blood, universal plasma donors have type AB blood (because they have neither anti-A nor anti-B antibodies in the plasma). 

How is my blood type determined?

The ABO system is based on antigens that are inherited. Meaning, like eye color, your blood type is passed on to you genetically from your parents. Whether you have AB blood type or group B blood or another blood group depends on the blood type of your mother and father. 

  • If both parents are O, you will have type O blood.
  • If one parent is O and the other parent is A, your blood group can be O or A.
  • If one parent is O and the other parent is B, you have O or B blood.
  • If one parent is O and the other parent is AB, your blood group can be A or B.
  • If both parents are A, you can be A or O.
  • If both parents are B, you can be blood group B or O.
  • If one parent is A and the other parent is B, you can be any ABO blood type (A, B, O, or AB).
  • If one parent is A and the other parent is AB, you can be A, B, or type AB blood.
  • If one parent is B and the other parent is AB, you can be A, B, or type AB blood.

What blood groups can receive my blood? 

For donations of blood cells:

  • Type O blood can be given to all.
  • Blood group A can be given to people with blood types A and AB.
  • Group B blood can be given to people with blood groups B and AB.
  • Group AB blood can be given to people with blood type AB only.

The rules for other blood products (plasma) are the opposite, i.e.; type AB can donate to all. 

So, if you have AB-positive blood, you are a universal plasma donor. You can donate plasma to all but red cells to people with type AB only. If you have type O negative blood, you can donate red cells to all and plasma only to the O blood group.

What blood types can I receive?

  • If you are blood group O, you can receive only O donor cells.
  • If you are blood type A, you can receive O and A.
  • If you are blood group B, you can receive O and B.
  • If you are group AB, you are a universal recipient and can receive all.

Also, Rh antigens need to be matched when you receive blood. People who are Rh-negative can only receive RhD antigen-negative blood. People who are Rh-positive can receive either RhD antigens (Rh-positive or Rh-negative blood). 

What is the healthiest blood type?

Certain diseases are more common in certain blood groups. For example, people with type O blood have the lowest risk for heart disease, and those with types B and AB have the greatest risk. Studies have also shown that people with A or AB blood groups are at higher risk of stomach cancer. Those with A, B, or AB blood types have a higher risk of pancreatic cancer. People with type A blood have more trouble handling stress. 

While your blood group is genetically determined and is not something you can change, you can reduce your risk for heart disease, cancer, and other health conditions by making healthy diet, exercise, and stress management choices.


  1. https://www.nhs.uk/conditions/blood-groups/#
  2. https://www.redcrossblood.org/donate-blood/blood-types.html
  3. https://www.redcrossblood.org/donate-blood/how-to-donate/how-blood-donations-help/blood-needs-blood-supply.html
  4. https://www.nm.org/healthbeat/healthy-tips/what-does-your-blood-type-mean-for-your-health#