Is There an Optimal Hemoglobin Level?

Abstract

THE RED CELL mass is an organ suspended in plasma and designed almost exclusively for the purpose of carrying oxygen from the lungs to the tissues. It is composed of erythron units, each originating from a proerythroblast. This precursor cell matures, synthesizes hemoglobin, and over a period of 4 to 5 days, undergoes four mitotic divisions resultingin the formation of 16 long-lived red blood cells (Fig 1). The marrow precursor cells are the end product of erythroid marrow progenitor cells. Our current concept of the kinetics of progenitor cells is that they are derived from a pool of multipotential stem cells capable of lifelong self-renewal (Fig 1). These stem cells can differentiate into a number of unipotential progenitor cells, including the erythroid progenitors. The early erythroid progenitors, the burst forming cells-erythroid (BFU-E), have only a limited capacity for self-renewal, and depend to a great extent on influx of cells from the stem-cell pool. In the presence of various nonspecific growth factors such as granulocyte monocyte-eolony stimulating factor (GM-CSF), interleukin-3 (IL-3), and erythropoietin, they will mature and multiply until they reach an end-stage, the colony forming unit-erythroid (CFU-E). In the presence ofthe erythropoietic hormone, erythropoietin, some of these cells will undergo blast transformation to a proerythroblast and start the formation of a new erythron. The total size of the red cell mass can be measured accurately by labeling a small number of red cells with various isotopes, primarily chromium 51, and determining the dilution of label 10 to 15 minutes after their infusion. The major problem with this technique is in the expression of the measured volume in a meaningful manner. The measurement is most often expressed in milliliters per