There are two blood group systems commonly used in clinical practice, one is the ABO blood group system and the other is the RH blood group system. the ABO blood group system is commonly referred to as blood type A, B, AB or O, etc., while the RH blood group system includes RH negative and RH positive. Generally, if the red blood cell surface contains RH antigen is RH positive, if it does not contain this antigen is called RH negative. rh antibody is a kind of incomplete antibody, in RH antigen, D antigen is stronger antigenic, the highest frequency, the clinical significance is greater, so according to D antigen can be roughly divided into RHD positive and RHD negative two. The detection methods are saline agglutination test or colloidal media method, simply put, RH blood group identification is to draw peripheral blood laboratory examination.