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Blood types are a classification of blood based on the antigens present on red blood cells. Antigens are molecules that can trigger an immune system response. There are eight common blood groups but 36 human blood groups in total.

A blood transfusion is a procedure that restores blood to the body. It is essential that people undergoing the procedure receive the correct blood type, or it will trigger the immune system, causing sickness and complications.

According to the American Red Cross, roughly every 2 seconds, a person in the United States requires a blood transfusion. They also note that this procedure saves 4.5 million lives each year.

In this article, we discuss the rarest and most common blood types by ethnicity.

Blood type definition 

People can define blood types using the ABO and Rhesus (Rh) blood group systems. These define blood types according to which antigens are present on red blood cells.

ABO system

This system classifies blood types as follows:

• Blood group A has A antigens on the red blood cells. 
• Blood group B has B antigens. 
• Blood group O has neither A nor B antigens.
• Blood group AB has both A and B antigens.

Rh system

Red blood cells may have another antigen called the Rh antigen on their surface. If it is present, the blood group is Rh-positive, but if it is absent, the blood group is Rh-negative.

Combining these two characteristics yields the eight most common blood types. Most people have one of these types:

• O-positive
• O-negative
• A-positive
• A-negative
• B-positive
• B-negative
• AB-positive
• AB-negative

The genes that a person inherits from their parents determine the mix of antigens and proteins in their blood. Due to this genetic factor, the American Red Cross suggest that when people need blood, especially those with rare blood types, the best matches tend to come from people of the same race or ethnic background.

Inherited characteristics, such as blood types, tend to run in ethnic groups. To increase the likelihood of well-matched blood types, experts recommend matching donors and recipients along ethnic lines, particularly for rare blood types. For this reason, some blood centers collect ethnic information from blood donors.

For some conditions, such as thalassemia and sickle cell disease, this matching is even more important because these conditions are more common among certain ethnic communities, and people may need frequent transfusions.

For example, only 2% of donors have a rare subtype of blood that doctors often use to treat sickle cell disease, but demand for it is increasing by 10–15% each year. The rarity of and demand for this type of blood emphasize the importance of blood donors.