Non-transferrin-bound serum iron (NTBI) in megaloblastic anemia: effect of vitamin B(12) treatment.

INTRODUCTION The abnormalities in iron metabolism associated with megaloblastic anemia are rapidly reversed by B(12) therapy in pernicious anemia (PA). Although non-tranferrin-bound plasma iron (NTBI) was previously shown to be associated with severe iron overload, its origin is unknown. METHODS AND RESULTS Four patients with PA were studied before and after B(12) treatment. NTBI was measured by a fluorescence-based one-step assay. All patients had very high transferrin saturation, NTBI values ranging from 1.1 to 2.6 micromol/l and normal serum ferritins. B(12) treatment resulted in the disappearance of NTBI and normalization of transferrin saturation within 22-42 h. CONCLUSIONS The prompt disappearance of NTBI following B(12) therapy implicates catabolic iron derived from ineffective erythropoiesis as the major source of NTBI in untreated PA and possibly in thalassemia major and sideroblastic anemia. Our findings offer further insight into the pathogenesis of NTBI in diseases associated with abnormal erythropoiesis.