Rh blood type checks for the Rh antigen (also called the Rh factor) on red blood cells. If your red blood cells:
Have the Rh antigen, your blood is Rh-positive.
Do not have the Rh antigen, your blood is Rh-negative.
For example, if you have the A and Rh antigens, your blood type is A-positive (A+). If your blood has the B antigen but not the Rh antigen, your blood type is B-negative (B–).