The presence or absence of certain protein molecules called antigens and antibodies determines the differences in human blood. Individuals have different types and combinations of these molecules. Your blood group depends on what you have inherited from your parents.
There are four major blood types: A. B. AB, and O. Each is divided into Rh positive or negative types. Every person has one of the above blood types. Also, every person's blood is either Rh-positive or Rh-negative. So, if you have type A blood, it's either A positive or A negative.
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Blood group A: with A antigens on the surface of your red blood cells and B antibodies in your blood plasma.
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Blood group B: with B antigens on the surface of your red blood cells and A antibodies in your blood plasma.
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Blood group AB: with both A and B antigens on the surface of your red blood cells and no A or B antibodies at all in your blood plasma.
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Blood group O: with neither A or B antigens on the surface of your red blood cells but both A and B antibodies in your blood plasma.
Blood type is a critical piece of information in blood transfusion. The blood used in a transfusion must work with your blood type. If it doesn't, antibodies in your blood attack the new blood and make you sick.
Type O blood is safe for almost everyone. About 40 percent the population has type O blood. People with this blood type are called universal donors. Type O blood is used for emergencies when there's no time to test a person's blood type.
People with type AB blood are called universal recipients. This means they can get any type of blood.
If you have Rh-positive blood, you can get Rh-positive or Rh-negative blood. But if you have Rh-negative blood, you should get only Rh-negative blood. Rh-negative blood is used for emergencies when there's no time to test a person's Rh type.
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