Blood type tests categorize your blood according to the major human blood group (ABO)

system. A person's ABO type depends upon the presence or absence of two genes — the A

and B genes. These genes determine part of the configuration of the red blood cell surface

Possible ABO blood groups include O, A, B, or AB.

The Rh antigen is another compound that may or may not be present on the surface of red

blood cells. The Rh test determines whether this configuration is present ("Rh-positive") or.

absent ("Rh-negative") on an individual's blood cells.