Blood types explained
Learn about the eight main blood types, including A, B, AB and O positive and negative, and why different blood groups are needed.
Your blood type is determined by molecules called antigens on the surface of your red blood cells and antibodies in your plasma. The two systems most people know are the ABO blood group system and the Rh system.
The eight main blood types
| Blood type | Rh status |
|---|---|
| A positive | Positive |
| A negative | Negative |
| B positive | Positive |
| B negative | Negative |
| AB positive | Positive |
| AB negative | Negative |
| O positive | Positive |
| O negative | Negative |
A positive and A negative
People with type A blood have A antigens on their red blood cells. A positive blood is Rh positive, while A negative blood is Rh negative.
B positive and B negative
People with type B blood have B antigens on their red blood cells. The positive or negative designation refers to the Rh system.
AB positive and AB negative
AB blood has both A and B antigens. AB positive and AB negative are distinct blood types with different compatibility characteristics.
O positive and O negative
O red blood cells do not carry A or B antigens. O negative red cells are often described as the universal red-cell donor type, which is one reason maintaining supplies can be particularly important in emergency situations.
Why do blood services need different blood types?
Hospitals need a reliable supply of different blood groups. Demand is affected by patient needs, clinical use and the characteristics of particular blood groups.
What is Ro blood?
Ro is a blood-group subtype within the Rh system. It is particularly important because closely matched blood can be needed for some patients who receive regular transfusions, including people with sickle cell disease.
Don't know your blood type?
Many people do not know their blood type before becoming a donor. Your blood group can be determined as part of the donation process.