TFRC and hyperinsulinemic hypoglycemia, familial, 4: However, if both ferritin and sTfR were measured, it may be advantageous to calculate TBI as it is expressed on the basis of body weight and, thus, allow for an evaluation of the full range of iron status from deficiency to excess within a population, thereby providing information on iron status beyond that of ferritin or sTfR alone (17).