Nephrology Dialysis Transplantation, Vol 13, Issue 90002 9-12, Copyright © 1998 by Oxford University Press
R Schaefer and L Schaefer
A number of factors have been shown to limit the response to recombinant
human erythropoietin (r-HuEPO). On major factor appears to be an inadequate
iron supply to the bone marrow. Erythropoiesis is dependent upon a
continuous supply of iron to the bone marrow. The rate at which iron can be
drawn from existing stores may easily limit the rate of delivery for
haemoglobin synthesis. This results in 'functional iron deficiency' caused
by depletion of iron stores. At present there are three main parameters
available to clinicians wishing to monitor iron status in their patients:
serum ferritin and transferrin saturation (TFS), which are indirect
measurements, and the percentage of hypochromic red cells, which directly
reflects marrow iron status. Ferritin levels should be measured before
starting r-HuEPO therapy to ensure adequate iron stores (<200
&mgr;g/l), and when patients move from the correction phase to the
maintenance phase of therapy (have stores become depleted during the
correction phase?). In addition, ferritin levels can give an indication of
iron overload following excess parenteral iron administration. The TFS
represents a balance between iron supply by stores and demand by bone
marrow. A saturation below 20% probably indicates iron-deficient
erythropoiesis. However, this is an indirect measure of marrow iron supply
and wide fluctuations have been observed when determined at different time
points. The percentage of hypochromic red blood cells is measured by flow
cytometry and a hypochromic subpopulation of more than 10% (normal
percentage <2.5%) indicates iron-deficient erythropoiesis. However,
not all departments may have access to the required equipment. The aim of
iron supplementation is to provide sufficient iron for the correction phase
and to replace iron losses (1500-2000 mg/year in haemodialysis patients)
during the maintenance phase of r-HuEPO therapy. This amounts to a daily
iron need in the range of 5-7 mg, which is well above the normal dietary
intake and absorptive capacity of the human intestine. Therefore there is a
need for intravenous iron, in particular when the patient has absolute or
functional iron deficiency, is intolerant of oral iron, or is not complying
well with the oral regimen.Key words: ferritin,
hypochromic red blood cells, iron, r-HuEPO, transferrin saturation
ORIGINAL ARTICLES
Iron monitoring and supplementation: how do we achieve the best results?
Med. Poliklinik D, Universitat Munster, Albert-Schweitzer-Strasse 33, 48129 Munster, Germany; Corresponding author
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