The plasma⁵⁹Fe clearance curve in man - An evaluation of methods of measurement and analysis

Studies of⁵⁹Fe clearance from the plasma are used for obtaining a quantitative measure of erythropoiesis. However, there are many difficulties associated with a good definition and a valid analysis of the plasma⁵⁹Fe clearance curve. The low plasma activity, plasma iron variation, and traces of haemolysis are factors which make the measurement of the curve difficult. All these problems were examined in the present work. Liquid scintillation counting allows a more accurate assay of plasma⁵⁹Fe activity than conventional gamma counting. Plasma iron fluctuations may affect tracer kinetics but adjustment of plasma activity for plasma iron variation (expressing⁵⁹Fe activity per unit mass of iron) does not appear a satisfactory procedure for overcoming this difficulty. The removal of haemoglobin from plasma samples is a necessary procedure to avoid contamination by [⁵⁹Fe] haemoglobin. Fitting three exponentials to the plasma⁵⁹Fe clearance curve does not yield satisfactory results in some cases. A better prediction of the clearance curve in most cases can be obtained by means of a more refined mathematical model.