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Why It’s Important to Know Your Blood Type

Jennifer Clements, MD, MSEd, NBHWCPatricia Pinto-Garcia, MD, MPH
Published on February 14, 2022

Key takeaways:

  • There are four blood types: A, B, AB, and O. Each blood type also has a positive or negative.

  • Some blood types are more common than others. People with rare blood types might have trouble finding a match for a blood transfusion.

  • Blood can’t be made in a lab, so people depend on donations for lifesaving treatments. Consider helping out people in need by participating in a blood drive!

Close-up of a blood group test on a paper card.
wakila/iStock via Getty Images

There are a number of different ways to learn your blood type. You might have found out your blood type from a finger prick in science class, a test before a medical procedure, or perhaps your parents told you. At some point, most people learn this important and unique information about themselves. 

There are plenty of practical reasons to know your blood type. For example, there’s ongoing research into whether your blood type can provide information about things like food sensitivities or whether you’re more likely to contract malaria or have complications from COVID-19. Knowing your blood type can also help you decide if you should donate blood, which is especially during blood shortages.

So you might be wondering what your blood type actually means. Here’s everything you’ve always wanted to know about blood types. 

What are the components of blood?

Let’s start with the basics: What exactly is blood anyway? Your blood — that red liquid that comes out when you get a cut — is made up of four things:

  1. Plasma: This is the “liquid” of your blood, which contains immunoglobulins, coagulation factors, and other important proteins.

  2. White blood cells: These cells fight off infections.

  3. Red blood cells: These cells carry oxygen to the rest of your body.

  4. Platelets: These are cell fragments that form blood clots.

What does it mean to have a certain blood type?

Your blood type describes the specific proteins that exist on your red blood cells. So even though there are four components in your blood, only the red blood cells determine your blood type.

Over time, your body will make antibodies only against the proteins that your blood cells don’t have. That way, your immune system doesn’t attack your own blood cells. Instead, it will attack anything that shouldn’t be in your body. While that function is usually very helpful, it can also cause serious problems.

Before scientists discovered these proteins, people used to have severe reactions to blood transfusions — but no one knew why. Once they identified blood types, healthcare providers were able to match donor and recipient blood types. And these transfusion reactions became a thing of the past. As scientists learned more about these proteins, they also figured out how to safely perform organ and tissue transplants. 

How many blood types are there?

There are four blood types

  1. A

  2. B

  3. AB

  4. O

These letters describe the first protein group that was discovered on red blood cells. But since discovering this group of proteins in the early 1960s, scientists have found about 600 other proteins

Thankfully, science decided to stick with the original blood types, which makes things a little less confusing. But in the event that you need a blood transfusion or a transplant, your healthcare team will test your blood (and your donor’s blood) for all of the different proteins. 

The rest of the time, when you get a test for your blood type — you’re being tested for your ABO type plus Rh type. 

What does a negative or positive blood type mean?

The “positive” (+) or “negative” (-) on a blood type refers to the Rh type. Rh is another protein on red blood cells that researchers discovered decades ago. 

If you’re Rh positive, then you have the Rh protein on your red blood cells. If you’re Rh negative, then you don’t have the Rh protein on your red blood cells.

So in addition to an ABO type, you have an Rh type. That means you can be Type A positive or negative, Type B positive or negative, and so on. 

What is the most common blood type?

The most common blood is Type O-positive, which means that it’s always in demand.

What is the rarest blood type?

Type AB-negative blood is the rarest of the eight blood types. 

But when healthcare providers talk about “rare blood types,” they’re really referring to more than just the ABO and Rh group. Red blood cells have many other proteins, and people with truly rare blood types don’t have antibodies against some or many of these. That means they can donate blood to people who have serious medical conditions or need multiple blood transfusions. 

Because genetics determine these proteins, some rare blood types are only found in certain groups of people. That’s why it’s so important for the diversity of blood donors to match the diversity of the community. 

Why is blood type important for blood transfusions?

Matching blood types keeps people from developing severe and life-threatening reactions during blood transfusions. If you need a blood transfusion (even in an emergency) and you don’t know your blood type — don’t panic. Your healthcare team will always check your blood type before giving you a blood transfusion, even if you already know your blood type.

How can I find out what my blood type is?

Your healthcare provider can order a blood test to determine your blood type. You can also request a blood type test from many online health platforms. Unless it’s medically necessary, your insurance might not cover the test. That means you’ll probably need to pay for the test if you’re just curious to know your blood type. 

You can also find out your blood type — for free — when you donate blood.

Why you should consider donating blood

In January 2022, the American Red Cross declared a blood shortage crisis. Healthcare providers are delaying surgeries and people are going without transfusions because there aren’t enough blood donations.

A blood transfusion is needed every 2 seconds in the U.S., and a blood donation is only good for 42 days. There’s no way to make blood — it only comes from donations. So if people aren’t donating, there’s just no way to keep up with the need.

Once you know your blood type, there are some facts to consider:

  • Type O negative: You are the universal blood donor. Anyone can receive your blood. Emergency rooms and operating rooms everywhere stock your blood type to use in case of a crisis. You have the preferred blood type to give to premature babies who don’t have fully formed immune systems, and you may qualify for the “Heroes for Babies” program.

  • Type O positive: You have the most common blood type. Your blood type is always in demand — it’s the most needed. If you also test negative for antibodies for cytomegalovirus (CMV), you’re eligible for the “Heroes for Babies” program.

  • Type A positive: You have the second most common blood type, and there’s always a need for your blood type. You should also consider platelet donation

  • Type A negative or B negative: Your blood type is less common than your positive counterparts, and you may be eligible for a ”Power Red” donation. Only 2% of people are Type B negative, and you can make a huge impact by donating blood. For those with Type A-negative blood, you should consider platelet donation, too. 

  • Type AB positive or AB negative: Your blood type is rare. Your blood donation is definitely welcome, although you will help more people by donating your plasma instead. Plasma donations are lifesaving and in short supply. 

  • Rare blood types: When you donate blood, the lab will check to see if you have a rare blood type. You might end up being a diamond donor!

To learn more about blood donation or to find a blood drive near you, you can visit the American Red Cross

The bottom line

There are 8 major blood types, but there are actually 600 proteins on your red blood cells.

Your blood type is an important part of who you are, but it also has the power to save lives. Blood donations depend on continuous donor participation, and right now the need is higher than ever. Consider donating blood, plasma, or platelets. It’ll let you find out your blood type — and you can also make a huge impact in your community. 


American Red Cross. (n.d.). AB elite plasma donation.

American Red Cross. (n.d.). Diversity in blood types.

View All References (11)

American Red Cross. (n.d.). Donate blood for babies.

American Red Cross. (n.d.). Find a drive.

American Red Cross. (n.d.). Platelet donation.

American Red Cross. (n.d.). Power red donation.

American Red Cross. (n.d.). ​​Why is type O blood so important.

American Red Cross. (2022). Red Cross declares first-ever blood crisis amid Omicron surge.

American Society of Hematology. (n.d.). Blood basics.

International Society of Blood Transfusion. (n.d.). Red cell immunogenetics and blood group terminology.

MedlinePlus. (2021). Blood.

National Health Service Blood and Transplant. (n.d.). Rare blood types.

National Heart, Lung, and Blood Institute. (n.d.). Rh incompatibility.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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