Blood Types

Although all blood is made of the same basic elements, not all blood is alike. In fact, there are eight different common blood type,  which is determined by the presence or absence of certain antigens_ substances that can trigger an immune response if they are foreign to the body.since some antigens can trigger a patient's immune system to attack the transfixed blood, safe blood transfusions depend on careful blood typing and cross _matching.

The ABO  blood Group System

There are four major blood groups determined by the presence or absence of two antigens_ A and B_ on the surface of red blood cells:

Group A_has only the A antigen on red cells(and B antibody in the plasma)

Group B_ has only the B antigen on red cells( and A antibody in the plasma)
Group AB_ has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
Group O_ has neither A nor B antigens on red cells( but both A and B antibody are in plasma)

There are very specific ways in which blood type must be matched for a safe transfusion.

Group O can donate red blood cells to anybody. It is the universal donor.

Group A can donate red blood cells to A's and AB's.

 Group B can donate red blood cells to B's and AB's

Group AB can donate to other AB's but can receive from all others.

In addition to the A and B antigens, there is a third antigen called the Rh factor, which can be either present( +) or absent ( _). In general, Rh-negative blood is given to Rh_ negative patients and Rh positive blood or Rh negative blood may be given to Rh positive patients.

Blood Types and the population

O positive is the most common blood type. Not all ethnic groups have the same mix of these blood types.Hispanic people, for example, have a relatively high number of O's, while Asian people have a  relatively high number of  B's. The mix of the different blood typed in the U.S. population is:


Caucasians.      African.   Hispanic.   Asian
 37%                   American
                            47%              53%           39%
8%                       4%               4%              1%
33%                     24%             29%            27%
7%                        2%               2%              0.5%
9%                        18%              9%             25%
2%                         1%               1%              0.4%
3%                          4%               2%              7%
1%                          0.3%            0.2%            0.1%


Some patients require a closer blood match than provided by the ABO positive/ negative blood typing. For example, sometimes if the donor and recipient are from the same ethnic background the chance of a reaction can be reduced. That's why an African_American blood donation may be the best hope for the needs of patients with sickle cell disease, 89 percent of whom are of African_American descent.