The blood group negative positive is for Rh blood group, because there are two types of Rh blood group in human body, Rh positive and Rh negative, this Rh blood group is different from ABO blood group, ABO blood group is clinically divided into A blood type, B blood type, AB blood type and O blood type, while Rh blood group system is only divided into positive and negative. rh positive means that there is D antigen on the red blood cell membrane, Rh negative means that there is no D antigen on the red blood cell membrane. There is no D antigen on the red blood cell membrane. At the same time, the proportion of Rh-negative people in our population is small, and RH-negative people can only receive Rh-negative blood in clinical blood transfusions. However, Rh-positive people can receive Rh-negative blood without hemolytic reactions. Therefore, Rh-negative people sometimes experience blood supply tension.