Problems in Ferrokinetics: extra radio-iron fixation to red cells

Red cell radio-iron utilization (RCU) exceeds the ratio red cell iron per whole-body iron due to the extra red cell fixation of radio-iron refluxed from tissue. The extra red cell radio-iron fixation reduces the radio-iron distribution to non-erythron tissue. Affected by RCU, the red cell iron turnover rate (RCIT) becomes larger than the net red cell iron turnover rate, which is indicated by the red cell iron renewal rate (RCIR). To clarify the influences of such biased radio-iron distributions, the values assayed by ferrokinetics were compared with those assayed by the methods other than ferrokinetics. The results showed the underestimation of the tissue and storage iron turnover rates in all cases determined using RCIT by ferrokinetics. All the previous investigators of ferrokinetics probably misunderstood the excess of RCIT as an iron turnover rate of the reflux from a labile iron pool in erythroblasts in normal subjects. However, such a reflux from erythroblasts is unlikely to exist in normal subjects with rapid and effective erythropoiesis. Influences on the iron turnover rates by the extra radio-iron distribution to red cell mass in iron deficiency anemia and by the radio-iron fixation to storage in hereditary hemochromatosis were also discussed from a new perspective.