Although all blood contains the same basic components (red cells, white cells, platelets, and plasma), not everyone has the same types of markers on the surface of their red blood cells. These markers (also called antigens) are proteins and sugars that our bodies use to identify the blood cells as belonging in our own system.
Blood cell markers are microscopic. But they can make the difference between blood being accepted or rejected after a transfusion. So medical experts group blood into types based on the different markers. Some people have an additional marker, called Rh factor, in their blood. Because each of the four main blood groups (A, B, AB, and O) may or may not have Rh factor, scientists further classify blood as either “positive” (meaning it has Rh factor) or “negative” (without Rh factor).
The different markers that can be found in blood make up eight possible blood types:
- O negative: This blood type doesn’t have A or B markers, and it doesn’t have Rh factor.
- O positive: This blood type doesn’t have A or B markers, but it does have Rh factor. O positive blood is one of the two most common blood types (the other being A positive).
- A negative: This blood type has A marker only.
- A positive: This blood type has A marker and Rh factor, but not B marker. Along with O positive, it’s one of the two most common blood types.
- B negative: This blood type has B marker only.
- B positive: This blood type has B marker and Rh factor, but not A marker.
- AB negative: This blood type has A and B markers, but not Rh factor.
- AB positive: This blood type has all three types of markers — A, B, and Rh factor.
Blood banks and hospitals keep careful tabs on blood type to be sure that donated blood matches the blood type of the person receiving the transfusion. Giving someone the wrong blood type can cause serious health problems. Via Facebook.