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
Irish Blood Transfusion Service Service. The frequency of blood groups in Ireland is as follows: It is important that the IBTS collects enough O Rh D positive blood as almost half the population are that blood type. Donors with O Rh D negative are known as universal donors. Their blood can be transfused to patients of any other blood group in an emergency or if the patient's own blood group is unavailable. Because any patient can receive O Rh D negative blood, the IBTS need to have extra O Rh D negative blood available at all times. The service depends entirely on voluntary donations