Positive and Negative Blood

Blood is categorized by a letter and either a positive or negative. Blood uses the ABO grouping system for the letter and the Rh factor grouping system for the positive and negative. Positive blood has the Rh antigen present in it's blood plasma, but negative doesn't. People with negative blood can obtain the Rh antigen by receiving it through a tranfusion with another person and people with positive blood can receive blood from people with negative blood because they already have the Rh antigen.