The difference between Rh-positive and Rh-negative blood lies in the existence or nonexistence of a protein named the Rh factor on the exterior of red blood cells. When the protein is present, the blood is categorized as Rh-positive, and if it is not present, the blood is classified as Rh-negative. The terms positive or negative used in blood typing, such as O positive or A negative, signify the Rh status of the blood (3).