Blood type Rh positive means that one is positive in the Rh blood group system. In clinical practice, besides ABO blood group system, the most commonly used blood group system is Rh. Rh blood group system was first discovered from the red blood cell membranes of Indian rhesus monkeys, and it was found that on the red blood cell membranes, those with D antigen are Rh positive and those without D antigen are Rh negative. Rh blood group has a very important significance in clinical transfusion, as Rh negative patients can only be transfused with Rh negative blood. Rh-positive people can be transfused with both Rh-positive and Rh-negative blood. However, because Rh-negative patients are very rare, Rh-negative patients often have difficulty in obtaining blood for transfusion.