Packed red blood cells Rh type, specifically the phenotype, and the "screen" refers to testing for atypical antibodies that might cause transfusion problems. The typing and screening are also performed on donor blood. The blood groups represent antigens on the surface of the red blood cells which might react with antibodies in the recipient. The ABO blood group system has four basic phenotypes: O, A, B, and AB. In the former Soviet Union these were called I, II, III, and IV, respectively. There are two important antigens in the system: A and B. Red cells without A or B are called type O, and
Rh blood group system the ISBT terminology) is not an accurate reflection of the antigens encountered since many (e.g. Rh38) have been combined, reassigned to other groups, or otherwise removed. Rh antibodies are IgG antibodies which are acquired through exposure to Rh-positive blood (generally either through pregnancy or transfusion of blood products). The D antigen is the most immunogenic of all the non-ABO antigens. Approximately 80% of individuals who are D-negative and exposed to a single D-positive unit will produce an anti-D antibody. The percentage of alloimmunization is significantly reduced in patients who are actively exsanguinating. All Rh antibodies "except" D display dosage (antibody