Measurement of plasma volume using 59Fe-labelled transferrin

A comparison of the plasma dilution volumes of specifically labelled [59Fe] transferrin and [125I] albumin in patients with a variety of haematological disorders has shown that, when transferrin is solely and specifically labelled with 59Fe, it has the same distribution volume as albumin over a wide range of values. Activities were measured in plasma samples collected at 10, 30 and 60 min after the initial injection and the fractional clearance rate of 59Fe was between 4 and 40 times faster than that of 125I. 59Fe is less expensive for routine investigations, and the use of the patient's own plasma may be more acceptable. (U.K.)