[Purpose] The evaluation of iron metabolism in the treatment of renal anemia is recommended based on serum ferritin levels, which reflect the body’s stored iron, but no reference value for ferritin has been established to determine iron deficiency/excess. In this study, we examined the usefulness of the total body iron (TBI) estimation formula in healthy subjects proposed by Cable for hemodialysis patients. [Method] TBI is calculated as the sum of the two major compartments of iron in the body： hemoglobin iron and stored iron. First, TBI calculated on test day ① was set as the reference TBI, and then on test day ②, the estimated ferritin value calculated backward from hemoglobin using this reference TBI was compared with the actual measured ferritin value. In situations where iron metabolism forms a semi-closed system, TBI is constant and the estimated ferritin value agrees with the actual measured ferritin. However, the amount of iron in hemodialysis patients is not constant due to iron replacement and loss, so iron delivery is out of balance. This study examined the relationship between estimated ferritin and actual measured ferritin levels associated with fluctuating TBI in hemodialysis patients. [Results] In patients with diverse clinical backgrounds, estimated ferritin showed a universal relationship with measured ferritin depending on the rate of change in TBI. Thus, the TBI formula was considered a reasonable equation that can be extrapolated to hemodialysis patients. [Conclusion] TBI is expected as a novel surrogate marker of iron metabolism to evaluate iron deficiency, maldistribution, and excess based on absolute values of hemoglobin iron and stored iron, which are difficult to assess by serum ferritin levels.