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Rheological properties were studied of young and old human erythrocytes from healthy adults. Viscosity measurements of packed erythrocyte suspensions as well as filtration of cells through polycarbonate sieves show that young cells are more flexible than aged ones. Since deformability of erythrocytes is the product of cell shape, flexibility of the membrane and fluidity of the intracellular hemoglobin, we studied the manner in which these factors are relevant to the diminished flexibility of aged erythrocytes. The biconcave cell shape is maintained during the process of aging. The viscosity of packed ghost suspensions from aged erythrocytes is increased versus that of young ones. The diminished flexibility of old ghosts correlates well with their smaller cell volume. The fluidity of the hemoglobin in the interior of the cells is decreased as indicated by an increased hemoglobin content of the isolated ghosts. We conclude that aged erythrocytes loose their deformability as a result of both a decreased fluidity of the intracellular hemoglobin and a diminished flexibility of the membrane.

Five patients, 11 months to 3 4/12 years old with severe normochromic, normocytis anemia and reticulocytopenia are reported. At the height of erythropoietic arrest when erythroid precursor cells were completely absent, undifferentiated stem cells (transitional cells), accumulated in the bone marrow. They disappeared again upon spontaneous resumption of erythropoiesis. We suggest that the erythropoietic arrest had occurred at the level of the hematopoietic stem cell. All patients recovered within 1 week of diagnosis. No steroid therapy was given. Failure to recognize this clinical entity leads to unnecessary diagnostic and therapeutic procedures including the transfusion of blood.