The blood composition of man is nearly similar to rhesus monkey. There are 6 common types of Rh antigen, each of which is known as Rh factor. They are designated as C, D, E, c, d and e. The type D antigen is widely prevalent in population. Anyone who has this type of antigen is said to be Rh+, whereas a person who does not have type D antigen is said to be Rh-.