Desferrioxamine chelatable body iron.

Further experience with the differential ferrioxamine test (Fielding, 1965) for the measurement of body-iron chelation has led to modifications which include (1) an improved standard for the estimation of ferrioxamine, (2) simplified preparation of the test dose, (3) restriction of fluid during the test and (4) simplified methods of calculation. The principle of the test remains the same: an intravenous injection is given consisting of two components, the chelating agent desferrioxamine, and the iron chelate ferrioxamine, labelled with approximately 2 ,uC "Fe. The urinary excretion of injected ferrioxamine is measured by isotope assay. Total ferrioxamine excretion is assayed chemically: this is derived both from injected ferrioxamine and from the action of desferrioxamine on body iron. The difference (Fd) between total ferrioxamine excretion (Ft) and ferrioxamine excreted from the test dose (Fex) represents the excretion derived from chelation in vivo. Total chelation in vivo (Fv) is then calculated by simple proportion from the isotope excretion data. The simultaneous injection of chelator and isotopelabelled metal chelate in the measurement of chelation in vivo produces a system which may be of wider interest in the study of chelation, not only of iron but of other metals. The characteristics of the system are: I The observed value depends on the ratio of urinary chelate excreted from two independent sources (Fd/ Fex): therefore, the timing of urine specimen collection is not critical since the ratio reaches a constant value in a relatively short time; thus, essentially the same result is obtained from a six-hour or seven-hour urine. 2 The results are independent of renal function, since both terms of the ratio are equally affected by variations in renal function. Thus, it is possible to study chelation in vivo in the presence of reduced renal function, provided sufficient excretion takes place to make chemical assay possible. 3 The results are not greatly affected by minor losses of urine during collection, since both terms of the ratio tend to be equally affected by such losses. 4 As shown below, the result is unaffected by variation in the volume of test dose within easily achieved limits.