The assessment of serum nontransferrin-bound iron in chelation therapy andiron supplementation

Nontransferrin-bound iron (NTBI) appears in the serum of individuals with i ron overload and in a variety of other pathologic conditions. Because NTBI constitutes a labile form of iron, it might underlie some of the biologic d amage associated with iron overload. We have developed a simple method for NTBI determination, which operates in a 96-well enzyme-linked immunosorbent assay format with sensitivity comparable to that of previous assays. A wea k ligand, oxalic acid, mobilizes the NTBI and mediates its transfer to the iron chelator deferoxamine (DFO) immobilized on the plate. The amount of DF O-bound iron, originating from NTBI, is quantitatively revealed in a fluore scence plate reader by the fluorescent metallosensor calcein, No NTBI is fo und in normal sera because transferrin-bound iron is not detected in the as say. Thalassemic sera contained NTBI in 80% of the cases (range, 0.9-12.8 m u mol/L), In patients given intravenous infusions of DFO, NTBI initially be came undetectable due to the presence of DFO in the sera, but reappeared in 55% of the cases within an hour of cessation of the DFO infusion. This app arent rebound was attributable to the loss of DFO from the circulation and the possibility that a major portion of NTBI was not mobilized by DFO, NTBI was also found in patients with end-stage renal disease who were treated f or anemia with intravenous iron supplements and in patients with hereditary hemochromatosis, at respective frequencies of 22% and 69%. The availabilit y of a simple assay for monitoring NTBI could provide a useful index of iro n status during chelation and supplmentation treatments. (Blood, 2000;95:29 75-2982) 2000 by The American Society of Hematology.