Why Do We Have Different Blood Types?

Charlie (age 14) asked,

“Why do we have different blood types?”

Thanks for your great question, Charlie!

There are four main blood groups: A, B, AB, and O. Your blood type is determined by proteins or antigens (AN-tuh-jen) found on your red blood cells. If you have type A blood, you have the A antigen on your red blood cells. Type B blood has the B antigen, AB blood has both antigens, and O blood doesn’t have either antigen.

Your red blood cells can also have another antigen called Rh. Some people are Rh-positive, meaning they have the Rh antigen. Others do not have the Rh antigen, so they are Rh-negative.

If you have the A antigen and the Rh antigen on your red blood cells, you have A-positive (A+) blood. If you don’t have either the A, B, or Rh antigen on your red blood cells, then you have O-negative (O-) blood. Blood types can be labeled in other ways too, but this way is the most common.

Why Blood Types Matter

Sometimes, people get hurt or sick and lose a lot of blood. When this happens, they might need a blood transfusion, which is a transfer of donated blood to the person through an IV. This blood usually comes from a donation bank. (Most people can safely donate blood because our bodies naturally produce more blood cells over time.)

Doctors need to know your blood type before a blood transfusion because you can only receive blood that is compatible with your type. For example:

• People with type A blood can only receive type A or type O blood.
• People with type AB-positive blood are sometimes called universal recipients because they can receive blood from any blood type since they have both A and B antigens.
• People with type O blood are sometimes called universal donors because they can donate blood to anyone since they don’t have either antigen.

Where Blood Types Come From

Your blood type is determined by your genes, which have been passed down from your parents and grandparents all the way from Adam and Eve. As the first humans, Adam and Eve had all the genes necessary to produce offspring with a variety of traits, including different blood types.

Though our blood types may differ, we are all part of the human race!

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