Most of us have one of eight common blood types.
These are identified in two parts – by the presence or absence of antigens (denoted with the letters A, B, O or AB) and an Rh factor (positive or negative).
There are two types of antigens (A and B). Your blood group is determined by whether you have one of these (A and B), both (AB) or neither (O) present on the surface of your red blood cells.
Whether your blood type is positive or negative reflects whether you have (positive) or don’t have (negative) this Rh factor on your cell surface.
Why blood type matters
There are two common clinical reasons your care team would need to know your blood type: if you receive any blood products and during pregnancy.
That’s because your body will recognize these factors (antigens and Rh factor). Your body will either identify them as familiar and ignore them, or as foreign, triggering an immune system response.
If you receive a blood transfusion, you can only receive blood that doesn’t contain antigens or Rh factor you don’t already have.
“These antigens, or the proteins on your red blood cells, are what cause an immune response. If they recognize it as foreign, they will respond to it and try to eliminate it,” said Amy Marchetti, a blood bank manager at OSF HealthCare Saint Anthony Medical Center in Rockford.
Become a blood donor
Your body won’t respond to any of these proteins if you already have them in your own blood.
A person who is AB-positive has both antigen types, as well as the Rh factor. This person could receive blood from any of the common blood types without triggering an immune response. This makes them known as a universal recipient.
A person who is O-negative, however, has neither antigen, nor the Rh factor. This individual could safely receive blood only if the donor is also O-negative. However, because this blood type does not contain any proteins that would trigger a response in the other blood types. This is why O-negative is known as the universal donor.
Your blood type may also play a role in how your immune system responds to other antigens, such as viruses.
One study suggests that people with Type A blood may be more likely than those with Type O blood to develop COVID-19 if they are exposed to the virus SARS-CoV-2 – though experts say people with all blood types should practice precautions to avoid contracting the disease.
Blood type and pregnancy
While many babies don’t have the same blood type as their moms, certain combinations could put a pregnancy at risk.
“It’s important for women to know their blood type and Rh factor during pregnancy. If the mom is Rh negative and the baby is Rh positive, there’s a chance the mother’s body could mount an immune response and develop an antibody to the baby’s blood,” Amy said.
Learn your blood type
While you can find at-home blood tests online, talk with your doctor if you are interested in learning your blood type. Your provider can order a simple blood test.
Amy also recommends that anyone interested in learning their blood type consider donating blood.
“If you’re healthy, 17 or older and at least 110 pounds, you can donate blood. You can help your community out and find out your blood type at the same time,” she said.
Last Updated: August 22, 2022