For something that literally gives you life, blood is pretty mysterious. You don't really get to see what it's doing inside of you, and yet, it's got all this extra information about you. I mean, do you even know what type of blood you have? If you don't, you're not alone — but you might want to find out.
The most common blood type in the U.S. is O-positive. About 37% of caucasian people, 47% of African Americans, 53% of Latinx Americans, and 39% of Asian Americans have this blood type, according to The Red Cross. Type A-positive comes in second, and B-positive is third most common. There are also a bunch of very rare other blood types that are only found in people from specific ethnic groups.
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In general, people with type O-negative blood can donate blood to nearly anyone. That's why it's often referred to as the "universal donor." Other blood types don't have that ability, due to the potential presence of antigens (markers that indicate types of antibodies you produce) and their rhesus (Rh) factor, the element that makes them "positive" or "negative." Although people with Rh positive blood can receive either positive or negative donations, those who have Rh negative blood can only receive other Rh negative blood.
However, as Ruben A. Mesa, MD explains at the Mayo Clinic, O-negative isn't always a perfect universal blood type — it can still contain antibodies that are known to cause serious reactions in certain people. That's why it's still ideal to match a blood donation type to its recipient exactly, accounting for both antigen types and Rh factor. In an emergency situation, however, you may still be given O-negative blood.
On the other end of the equation, type AB is referred to as the "universal recipient" because people with this blood type can receive any type of blood. However, people with type O blood can only receive type O.
This is all to say that your blood type is a pretty important thing to know about yourself. If you're donating blood, you can rest assured that (in most cases) they'll test your blood to figure out what type it is. But if you're in an emergency and you need blood fast, knowing your blood type can help speed everything along. If you'd like to find out your blood type, you can call your doctor (who may have it on file) or ask for a blood type test along with your next routine blood exam. You'll learn a little more about yourself — information that could even save your life.