NONSPECIFIC SERUM IRON IN THALASSEMIA - QUANTITATION AND CHEMICAL-REACTIVITY

We reported earlier an abnormal iron population in the serum of patients with transfusional hemosiderosis secondary to thalassemia. The iron is not bound to transferrin, ferritin, or hemoglobin and is referred to as nonspecific iron. This publication reports studies of the chemical reactivity and nature of the nonspecific iron and the development and validation of a method for its quantitative analysis. The quantitation depends on the mobilization of this iron from nonspecific macromolecular binding sites by ethylenediamine tetraacetic acid and subsequent separation from Fe3+‐transferrin‐CO⅔− and residual hemoglobin by ultrafiltration. Analyses of filtrate iron were carried out by atomic absorption and colorimetric methods. The accuracy of the test was established via an ultrafiltration titration of serum of known unsaturated iron‐binding capacity. The method proved to be accurate and highly reproducible. Sera containing artificial introduced nonspecific iron were prepared. The reactivity of artificial and thalassemic nonspecific iron was examined with regard to reduction and chelation, and chelation by apotransferrin. Artificial and thalassemic nonspecific iron were found to be virtually identical in reactivity and to exhibit multiphasic kinetics consistent with nonspecific binding to several serum protein sites. The reaction of apotransferrin with nonspecific iron was complete within one minute. The reduction‐chelation and apotransferrin reactivity studies offer independent analyses of nonspecific serum iron concentrations which compared closely with the chelation‐ultrafiltration technique. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company