Do You Need to Know Your Blood Type?

Unless you’ve had a major surgery, been pregnant, or donated to a blood bank, you may not know your blood type. But should you?

“If I tattooed my blood type on my chest as a precaution, and I ended up in the emergency room in a life-threatening situation, they would ignore my tattoo and do a blood type test to make sure they get it right,” says hematologist Andrew Eisenberger, MD, an associate professor of medicine at Columbia. “Blood type is extremely important, but only in certain rare cases, and only to medical staff.”

What are blood types?

Blood types are based on markers on the surface of red blood cells. These markers—called A and B—determine your main blood group. You may have marker A (type A), marker B (type B), both (type AB), or neither (type O).

Some people also have another marker called Rh. If you have it, your blood type is positive; if you don’t, it’s negative. Together, these markers create eight possible blood types:

1. A positive: Common; can donate blood to A positive and AB positive
2. A negative: Rare; can donate blood to A and AB
3. B positive: Rare; can donate blood to B positive and AB positive
4. B negative: Very rare; can donate blood to B or AB
5. AB positive: Rare; can receive blood of any type, known as universal recipients
6. AB negative: The rarest; can donate blood to any type, known as universal plasma donors
7. O positive: Common; can donate blood to any positive blood type
8. O negative: Rare; can donate blood to any blood type; can only receive from other O negative

Your blood type is a result of your genes. Because there are many possible combinations of markers, you may not have the same blood type as your parents.

Why do medical providers need to know my blood type?

The markers on your blood cells work with your immune system. If you need a blood transfusion or organ transplant, the A and B markers on the new blood cells must be compatible with yours, or your immune system will attack them. The reaction is immediate and can be life-threatening, such as kidney failure.

It’s also important for your doctors to know your blood type if you’re pregnant. If you have a negative blood type but the fetus has a positive blood type, your immune system may see those positive markers as a threat. Your provider will give you medications to stop your immune system from attacking the fetus’s blood.

Should I know my blood type?

No. Even if you know your blood type, health care staff will always double check it before a procedure. It’s called ABO determination.

If you are experiencing life-threatening blood loss and staff do not have time for ABO determination results (which can take around 45 minutes), you will be given O blood.

How do I know I’ll get the right blood type in the hospital?

In the United States, there are about 14 million units of blood transfused every year. Hospitals must get it right because the stakes are high, and the systems are strong enough to prevent it from happening.

When blood gets typed, whoever drew the blood must sign the tube containing it. If there's no signature on a tube, the blood banks reject it—even if it has a label with name, medical record number, and barcode. Accountability is everything.

Is there a “best” blood type?

No. Blood types can influence other things in people's health, but there aren’t tremendous differences in life expectancy between the different blood groups.

Blood type plays a role in determining a person’s susceptibility to certain diseases and issues:

• People with certain blood types are slightly more at risk for getting more severe cases of COVID
• Blood type O have lower rates of developing blood clots in their legs and their lungs (deep vein thrombosis)
• Blood type AB has the highest rates of developing blood clots

If you are worried about severe COVID, you can get vaccinated. If you are worried about blood clots, you can wear compression socks on an airplane. Talk to your doctor to find out what is best for you.

The bottom line? It is not necessarily useful to know your blood type, but you’re encouraged to donate blood if you’re able.