Blood types

About 5 million Americans need blood transfusions every year, for all sorts of reasons. Sometimes, a transfusion is an emergency (like losing blood after an accident). Sometimes it’s expected (as with treatment for cancer).

Whatever the reason, blood transfusions are one of the most common hospital procedures.

While transfusions are common, there’s a lot more to them than just taking blood from one person and using it to help someone else. It’s very important to keep the blood supply safe. So, each unit of blood goes through many tests to check for infectious diseases and establish the blood type.

Four Blood Groups…

It might seem like blood is blood — it all looks pretty much the same to the naked eye. But 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.

The four main blood groups are:

1. Type A. This blood type has a marker known as “A.”
2. Type B. This blood type has a marker known as “B.”
3. Type AB. The blood cells in this type have both A and B markers.
4. Type O. This blood type has neither A or B markers.

…Make Eight Blood Types

The different markers that can be found in blood make up eight possible blood types:

1. O negative. This blood type doesn’t have A or B markers, and it doesn’t have Rh factor.
2. 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).
3. A negative. This blood type has A marker only.
4. 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.
5. B negative. This blood type has B marker only.
6. B positive. This blood type has B marker and Rh factor, but not A marker.
7. AB negative. This blood type has A and B markers, but not Rh factor.
8. AB positive. This blood type has all three types of markers — A, B, and Rh factor.