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What Makes Your Blood Type Unique?

For most people, knowing your blood type isn’t at the top of your medical priorities. Unless you’ve had a recent blood transfusion or pregnancy, there aren’t too many times you need to know this information. However, in the case of an accident or emergency it could be helpful to know your blood type.

Why Are Blood Types Different?

Blood is categorized into four main groups, A, B, AB and O.

What determines your blood type is an antigen on the red blood cell. An antigen is a small protein that creates an immune response in your body. There are two antigens, A and B, that determine your blood group depending on if the antigen is present or absent.

  • Type A blood has an A antigen on the red blood cells
  • Type B blood has a B antigen on the red blood cells.
  • Type AB blood has both A and B antigens.
  • Type O blood  has neither A nor B antigens.

The antigens in your blood and your blood type are determined by your genetics.

“These antigens don’t affect your health or the way your body functions, it is just a genetic difference like hair color or height,” said Josh Cumberland, lead medical lab scientist at Samaritan Albany General Hospital.

If you need a blood transfusion, it is important to get the right type. Your body will recognize blood with the same antigen and welcome it but if the donor blood has a different antigen, your body will treat the new blood as an invader and attack it. This immune response can lead to kidney damage or death if not treated right away. Fortunately, Cumberland noted, an incompatibility reaction is very rare since strict protocols are in place at medical facilities to ensure patients receive the right type of blood.

Unique Blood Types

While type A and B blood types are fairly straight forward, O and AB are unique. Type O has no antigens. That means that it can be given to anyone without a problem because there are no new antigens being introduced that may stimulate an immune response.

Those with AB blood have both the A and B antigen so they can receive blood from anyone with type A, B or O blood.

What About Positive & Negative?

In addition to the four main ABO groups you may have heard of blood that is positive or negative.

According to the American Society of Hematology, there are 35 major groups of antigens besides A and B. Some antigens are only found within certain racial or ethnic groups. Most antigens are benign – they won’t hurt you if you receive blood that contains it.

However, a group of antigens that is most likely to cause a reaction if not matched is called the Rh group, specifically RhD. You may also hear this called the Rh factor. If you have the Rh antigen in your blood you are Rh positive. If you do not, you are Rh negative.

Since Rh factor is the next antigen after ABO blood type most likely to cause complications, blood is further categorized into Rh positive or negative for a total of eight different blood types: A positive, A negative, B positive, B negative, AB positive, AB negative, and O positive or O negative.

Someone with A positive blood would have both an A antigen and an Rh antigen on their red blood cells, while those with A negative blood have an A antigen but no Rh antigen.

Blood Type & Pregnancy Concerns

When a woman is pregnant, having a blood test to see if she is Rh negative occurs early in her prenatal care. During delivery, the blood of the mother and the baby can sometimes mix. According to the American College of Obstetrics & Gynecology, if the baby is Rh positive and the mother is Rh negative it can cause the mother’s body to create antibodies, which can be a problem for future pregnancies. If the fetus in a future pregnancy is also a positive blood type, those antibodies in the mother can cross the placenta and attack the blood of the fetus as it grows, causing complications like anemia, jaundice or stillbirth.

“As part of routine care, a mother with Rh negative blood will receive a shot during her second trimester and another after delivery to prevent her body from making these antibodies,” said Maggie Hudson, a certified nurse midwife at Samaritan Obstetrics & Gynecology - Corvallis.

How Common Is Your Blood Type?

The Red Cross reports that O positive is the most common blood type, held by 38 percent of the population. Only one percent of the population has AB negative blood. 

Those with O negative blood make up a small percentage of the population but are the most in-demand as blood donors. Since they have no A, B or Rh antigens, their blood can be safely given in hospitals and emergency departments to people whose blood type is unknown.

 Blood Type Rh+ Rh-














How to Find Out Your Blood Type

Blood typing isn’t a part of routine blood work like a metabolic panel, so you would need to ask your clinician specifically for that to be tested, said Hudson. Check first to see if your insurance will cover it. If you’ve had a pregnancy since the advent of electronic medical records but have forgotten your blood type, you can always go back and check your test results in MyChart

For around $10, you can also purchase an at-home blood typing kit from the drugstore. Or you can donate blood, and the Red Cross will tell you your blood type for free.

“You’ll never receive subpar medical care if you don’t know your blood type, but it can be interesting information,” said Hudson. “There is always a need for blood at blood banks, so finding out your blood type can also be a good reason to donate.”

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