woman getting blood draw

Do You Need to Know Your Blood Type?

November 2, 2023
Dr. Andrew Eisenberger

Andrew Eisenberger, MD

Even though it runs through your veins, unless you had a major surgery, were pregnant, or have donated to a blood bank, you probably don’t 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 will ignore my tattoo to make sure they get it right,” says hematologist Andrew Eisenberger, MD, an associate professor of medicine at CUIMC. “Blood type is extremely important, but only in certain rare cases, and only to medical staff.”

We spoke to Eisenberger to find out more.

What are blood types?

Everyone’s blood has the same basic elements, but there are eight variations, known as blood types.

  1. A positive: Common; can donate blood to other 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 universal plasma donor
  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.

What do A, B, and O mean in blood type?

A and B are sugars (carbohydrates) on the surface of red blood cells. O means a lack of A and a lack of B.

Why is blood type important?

If something happens to you—an accident, illness, or injury that requires a blood transfusion—blood type is important because you want your body to accept the blood it receives.  

The A and B blood types are immunogenic: the body’s immune system will react to them if it doesn't know them.

If you’re blood type A, and you get A blood, your immune system recognizes the A sugar and doesn't react to it. But if you get blood type B, your immune system will see it as foreign and will attack those red blood cells. The reaction is immediate and can be life-threatening. Think kidney failure.

There’s more time when it comes to the positive and negative types. It takes 7 to 10 days to get the initial response. 

Either way, the systems are in place for blood type mistakes not to happen.

Is it important for someone to know their blood type?

No. You do not need to know your blood type. You don't need blood regularly. It’s beneficial information for the medical community but it is not beneficial to you.

Why not?

Even if you know your blood type, if you do anything with your blood, the type will need to be verified. If you donate blood, you may have a donor card with your type listed, but staff still needs to confirm. If you have a medical procedure, the staff needs to confirm. It’s called ABO determination.

If you are in an emergency, life-threatening, bleed-to-death situation and staff do not have time (usually around 45 minutes) for ABO determination results, you will be given O blood.

Men are given O positive. Women of childbearing age will get O negative blood. Negative blood types develop immune responses to positive blood, which can lead to an immune system attack on the red blood cells of a fetus, now and in a future pregnancy.

The most common procedure performed in a hospital is blood transfusion (you need it during open heart surgery, hip replacements, and other major procedures), but most people go through their lives not needing a blood transfusion.

Your blood type also affects who you can get organs from: for lungs, liver, kidney, and heart, you’ll need an organ from someone with a compatible blood type. But, again, most people will never need a solid organ transplant.

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

In the United States, there are about 14 million units of blood transfused every year. And the number of transfusions has gone down. We’ve realized people can do very well with lower blood counts and can avoid infections and other kinds of reactions.

That said, hospitals must get it right because the stakes are high. The number of incompatible transfusions in the United States is negligible because the systems are strong enough to prevent it from happening.

When blood gets typed, whoever drew the blood (the phlebotomist) 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 one blood type the best?

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

What else can blood type influence?

To start: There's nothing you can do about your blood type or the risks it influences.

We know 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

Again, there is nothing that can be done to change your blood type. Nor is it a reason to find out your type. 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.

People come to us who did ancestry or genetic tests, or when they got pregnant, or when their significant other is pregnant, who found out they have a rare condition or are a carrier for a rare condition. It rarely helps anyone to know. Most are in their 30s, 40s, 50s and never had any problems before, so this information creates a lot of noise and is not a useful signal.

Are blood-type diets beneficial?

You're welcome to eat this way, but I can't say that there's evidence to support it.


The bottom line? It is not useful to know your blood type, but it is encouraged to donate blood.



Andrew Eisenberger, MD, is an associate professor of medicine at CUIMC.