Deficiencies of iron, vitamin B12, or folic acid on the one hand and/or the presence of primary bone marrow disease on the other may result in a decreased production of red blood cells (Table 1). Underlying chronic diseases (i.e. malignancies, systemic diseases, metabolic disturbances) or (chronic) infections may also result in a decreased red cell production. Anemias in the latter group of disorders are characterized by an underproduction of red blood cells owing to a decreased availability of iron. Depletion of the body iron stores during chronic infection probably has an immunological etiology and is modulated by the production of cytokines. This mechanism is well demonstrated in some recent animal studies, suggesting that iron depletion has a protective effect in the critically ill septic patient ( Kent et al. 1994).
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