Plasma non-transferrin-bound iron (NTBI), first described in 1978,1 is a pathological iron pool detectable when Tf saturation exceeds 75%.2, 3, 4 NTBI appears when iron influx into the plasma compartment exceeds iron efflux, for example, with iron overload, ineffective erythropoiesis, or decreased transferrin iron clearance in erythroid hypoplasia.5 Here, TF is linked to Erythroid hypoplasia.