ABO blood groups are based on the presence or absence of certain antigenic substances on the surface of red blood cells. The main antigens are A and B, with O being the absence of both A and B.
Blood group O can be further divided into two subgroups: O positive and O negative.
Rh factor is another important component that’s determined by your genes. If you have Rh-positive blood, this means you have an Rh factor protein on the surface of your red blood cells; if you don’t have it (Rh-negative), then you’re considered Rh-negative as well as ABO-negative.« Back to Glossary Index