There are various human blood types, including ABO, RH, MN, P blood group blood and so on. Among them, the least blood system is found to be the P blood type system. The P blood type system is an independent blood system, different from the ABO and RH blood systems, and the P blood type system is divided into five types, such as P1, P2, P1k, P2k and P blood type, according to whether the red blood cell membrane contains P1 antigen or not, among which P blood type is the least blood type. Although P blood type is the least blood type, this is due to the fact that P blood type itself has obvious antigenicity, so people with this blood type can only receive P blood type, and if blood of other blood types is transfused, serious hemolytic reactions will occur. Because of this, people with P blood type often encounter difficulties in blood supply during clinical use, so P blood type is the least type in the human blood group system.