The Rh factor identifies the presence of the rhesus protein in blood. The Rh factor can be represented by a + or – sign. It is important to know the Rh factor because just like how the antigens on the blood must be compatible, the rhesus protein in blood must also be compatible. If a person has Rh+ blood they can receive Rh+Rh-Rh+ or Rh- blood.If a person has Rh- blood they can receive Rh+Rh-Rh + or Rh- blood.