The red blood cells (and other cells) contain many molecules, called blood group antigens that define certain properties of these cells. There are a number of blood groups, the most important of which are ABO and Rh blood groups.
The ABO blood group system includes A, B, AB and O, which are the four main blood types found in human erythrocytes.
The distribution of blood groups among our population is as follows:
After ABO, the most important blood group system is the Rh system.
All who have Rh factor on the erythrocytes are Rh positive (85% of the population), those who do not have Rh factor are Rh negative (15% of the population).