Nucleated red blood cell Nucleated red blood cell All vertebrate organisms have hemoglobin-containing cells in their blood and with the exception of mammals, all of these red blood cells contain a nucleus. Mammals represent ~5,500 named species out of ~66,000 vertebrate species, and within this ~8% subgroup, red blood cells are known as erythrocytes or RBCs and lack a cell nucleus in mature organisms. In contrast, a nucleated red blood cell (NRBC), also known by several other names, is a mammalian RBC that contains a cell nucleus. NRBCs occur in normal development as progenitor cells in the erythropoietic lineage and in pathological states. Normally,
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