A negative blood type means that a person’s blood type is A in the ABO blood group system and Rh negative in the RH blood group system. The ABO blood group system classifies human blood groups into A, B, AB and O according to the antigens on the red blood cell membrane, while the Rh blood group system classifies Rh blood groups into Rh-positive and Rh-negative according to the D antigen contained in the red blood cell membrane. The Rh blood grouping system classifies Rh-positive blood and Rh-negative blood according to whether or not the D antigen is contained on the red blood cell membrane, and Rh-positive blood is Rh-negative blood if it does not contain the D antigen. Therefore, A-negative blood means A blood type in the abo blood group system and Rh-negative blood in the Rh blood group system.