About Blood

Blood Types

ABO Types

The ABO blood groups are defined by the presence or absence of two inherited molecules, or antigens, A and B, that are present on the surface of red blood cells. You inherit either A or B antigens (group A or B), both A and B antigens (group AB), or neither antigen (group O).

The Rh system

Discovered 40 years after the identification of ABO blood groups, the Rh factor is the second most significant blood-group system in human-blood transfusion. The presence or absence of the D antigen on a red cell determines whether you are Rh+ or Rh-.

ABO and Rh distribution in the USA:

O+
37.4%
A+
35.7%
B+
8.5%
AB+
3.4%
O-
6.6%
A-
6.3%
B-
1.5%
AB-
0.6%