1. icon-arrow-left
    Healthy Living
Healthy Living · article

Should I know my blood type?

Blood tests

From pregnancy to blood transfusions to blood donations, there are many situations where your blood type is a critical piece of information in your care – and the care of others.

Sreevani Thota, MD, a primary care physician with Atlantic Health System, shares more about blood types and why it helps to know yours. 

What are blood types?

Your blood type is a combination of antigens, or markers, on your red blood cells, as well as an Rh factor, a different marker that can be found on the cell’s surface. You inherit both your antigen and Rh factor from your parents. There are four antigen combinations (A, B, AB and O). The Rh factor can either be positive, which means the protein is present on the cell’s surface, or negative when it isn’t.

With these combinations, there are eight common blood types:

  • A+
  • A-
  • B+
  • B-
  • AB+
  • AB-
  • O+
  • O-

In addition to these groups, there are many rare blood groups that do not fall under the ABO system. Most Americans have a positive Rh factor. The most common blood type in the U.S. is O+, while the least common is AB-.

You can find out your blood type during your next blood test in your doctor’s office or when you donate blood.

What blood types are compatible?

It’s important to know if your blood type is compatible with other blood types. That’s because your immune system will attack blood cells with antigens they don’t recognize, which can be very dangerous.

“Knowing your blood type is important if you are pregnant or if you find yourself in an emergency situation,” says Dr. Thota. “For example, receiving blood with the wrong antigen or a positive Rh factor if you are negative can be life-threatening. Having that information available can help your care team provide the right blood for you, quickly.”

Compatible blood types include:

  • A+: A+, A-, O+, O-
  • A-: A-, O-
  • B+: B+, B-, O+, O-
  • B-: B-, O-
  • AB+: A+, A-, B+, B-, AB+, AB-, O+, O- (universal recipient)
  • AB-: A-, B-, AB-, O-
  • O+: O+, O-
  • O-: O- (universal donor)

How are blood types used?

Knowing your blood type – and what other types are compatible — can be important in different situations including:

  • Blood donation: While blood donations of all types are nearly always needed, your local facility may need a particular blood type more than others. Donating blood can help save a life.
  • Blood transfusions: In cases including emergencies, surgeries or other major medical events, you may need to receive blood from a donor. If that blood is not compatible, it can cause dangerous complications.
  • Pregnancy: If a pregnant patient has a negative Rh factor and their fetus has a positive Rh factor, the mother’s immune system may try to attack the red blood cells of the fetus. Fortunately, expectant mothers are screened early in pregnancy and a simple shot called RhoGAM helps stop the immune system from responding to these cells.
Find a Primary Care DoctorDonate Blood
Published: February 12, 2025

Related articles

Healthy LivingCan diet and exercise lower your cancer risk?Learn how lifestyle modifications like diet and exercise can lower your cancer risk with practical advice from Atlantic Health System.
Healthy LivingShould I know my blood type?Knowing your blood type can be important for your health. Learn when — and why — this information can help with advice from Atlantic Health System
Healthy LivingDo we really need eight glasses of water a day?Do people need to drink water all day long to stay hydrated? We asked an expert at Atlantic Health System about the eight-glass-a-day rule for adults—and his answer may surprise you.
Healthy LivingLab test accuracy: what to know before getting bloodworkBefore you head to the lab for bloodwork, a little preparation will go a long way to ensure accurate results. Here are a few tips from an Atlantic Health System expert.
Healthy Living5 markers for optimal metabolic healthA well-functioning metabolism is the key to health and longevity. By tracking five simple biomarkers, you’ll better understand your metabolic health and how to improve it. Good metabolic health reduces chronic conditions like diabetes, heart disease, and obesity.
Healthy LivingCatch some ZZZs: healthy habits for a better bedtime routineAre your bedtime habits keeping you from getting a good night’s sleep? Learn about common sleep disorders and when you should see a sleep specialist.
Healthy LivingAre diabetes and strokes related? Learn why diabetes is a risk factor for having a stroke and ways to lower your risk of diabetes and stroke from a stroke expert at Atlantic Health System.
Healthy LivingEscaping reality: how to recognize video game addictionPlaying video games in moderation can have real benefits. But used in excess, it can become harmful. For some people, gaming can lead to social isolation, aggression, and even physical or mental health problems. Here are a few behavior patterns that might signal a gaming disorder.
Healthy LivingBrain over bladder: overcoming urinary incontinenceGoing to the bathroom doesn’t need to be stressful. Learn how to overcome urinary incontinence with tips from Atlantic Health System pelvic floor therapist, Jenna Silverman.
Healthy Living7 Ways to Ease Seasonal Affective Disorder (SAD) When winter weather turns cold and dark, it’s natural to become withdrawn and isolated. But if these behaviors negatively disrupt your life, it could be tied to a form of depression known as Seasonal Affective Disorder (SAD).
Healthy LivingFive signs of an unhealthy bladderThe health of your bladder can have a significant impact on your overall health. Learn more from an Atlantic Health System urologist.
Mental WellnessFive hidden signs of substance abuseIf you think someone you care about is overusing drugs or alcohol, pay attention to these five warning signs. Addictive behaviors endanger the user and the people around them. Knowing what to look for is the first step to getting the help they need.