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B12deficiency is the leading cause of megaloblastic anemia, and although more common in the elderly, can occur at any age. Clinical disease caused by B12deficiency usually connotes severe deficiency, resulting from a failure of the gastric or ileal phase of physiological B12absorption, best exemplified by the autoimmune disease pernicious anemia. There are many other causes of B12deficiency, which range from severe to mild. Mild deficiency usually results from failure to render food B12bioavailable or from dietary inadequacy. Although rarely resulting in megaloblastic anemia, mild deficiency may be associated with neurocognitive and other consequences. B12deficiency is best diagnosed using a combination of tests because none alone is completely reliable. The features of B12deficiency are variable and may be atypical. Timely diagnosis is important, and treatment is gratifying. Failure to diagnose B12deficiency can have dire consequences, usually neurological. This review is written from the perspective of a practicing hematologist.

Free erythrocyte porphyrin: hemoglobin (FEP: Hb) ratios were determined on 20 infants with iron-deficiency anemia. FEB:Hb ratios were compared with simultaneously drawn serum ferritin and serum transferrin saturation levels. FEP:Hb ratios dropped steadily during treatment of the anemic infants, but remained elevated compared to age-matched nonanemic infants, until the anemia was corrected. FEP:Hb ratios detected iron deficiency when acute inflammatory disease was present. Serum ferritin levels and transferrin saturation failed to detect iron deficiency after iron therapy was started or when acute inflammatory disease was present. Measurement of FEP:Hb ratios is a reliable and practical way to make a prompt diagnosis of iron-deficiency anemia in infants.

Monocytes and macrophages have receptors for the iron-binding protein lactoferrin. Lactoferrin acts as a potent inhibitor of granulocyte-macrophage colony stimulating factor production when it binds to these cells. Using a rosette assay and immunofluorescence, we have shown that cultured leukemia cells, including the human erythroid leukemia cell line K562, also have lactoferrin binding sites. The number of binding sites on K562 cells was estimated using soluble 59Fe-lactoferrin. Inhibition studies demonstrate that lactoferrin binding sites are distinct and unrelated to receptors for transferrin or the Fc portion of IgG, which are present on K562 cells. However, electrostatic forces may be important for lactoferrin binding, since other polycationic proteins (eg, protamine) inhibit lactoferrin binding. Prior treatment of K562 cells with trypsin nearly abolishes lactoferrin binding. However, these cells recover their ability to bind lactoferrin when trypsin is removed. Unlike transferrin receptors, the expression of lactoferrin binding sites is not regulated by cellular iron status. Cytosine arabinoside arrests the proliferation of K562 cells and simultaneously leads to a reduction in lactoferrin surface binding, suggesting that lactoferrin binding may be dependent on cell proliferation.

We have exploited the physiologic mechanism for removal of red cells from the circulation to target the iron chelator desferrioxamine to reticuloendothelial iron stores. Compared with free desferrioxamine injected intravenously, the same dose of desferrioxamine entrapped in resealed red blood cell ghosts resulted in a fourfold to fivefold increase in excretion of radioiron in rats with a selective 59Fe radiolabel of reticuloendothelial iron stores. Desferrioxamine in red cell ghosts did not enhance excretion in rats with selective radiolabeling of parenchymal iron stores. In rats with uniformly radiolabeled iron stores, desferrioxamine in red cell ghosts produced an eightfold to ninefold greater loss of iron in the urine than free desferrioxamine intravenously or by slow subcutaneous infusion. Desferrioxamine in red cell ghosts resulted in significantly greater fecal excretion of iron than intravenous desferrioxamine, but desferrioxamine in red cell ghosts and subcutaneous desferrioxamine infusion resulted in similar fecal iron excretion. Clinical application of the red cell ghost method for administration of desferrioxamine and other iron chelators may be useful for improvement of iron chelation efficiency.

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