MEASUREMENTS OF ABSOLUTE RADIOIODINE UPTAKE IN THE ASSESSMENT OF HUMAN THYROID ACTIVITY

Abstract

SUMMARY The uptake of radioiodine by the human thyroid 24 hr after a tracer dose of 25 μc. has been measured by means of a toroidal counter with a high sensitivity not critically dependent on the relative position of the source. The distribution of the 24 hr uptake values for males and females is given. Values of the sum of the 24 hr uptake and the 24 or 48 hr urinary excretion of radioiodine have been determined, and are shown to be distributed about a mean of 91% of the dose. With this information it has been possible to replace excretion measurements by uptake measurements in the computation of the thyroid index It described previously [Haigh & Reiss, 1950; Reiss, Haigh, Hemphill, Maggs, Reiss & Smith, 1952]. The new index I′t has the same dimensions as It, but the respective scales of thyroid activity, although similar, are not interchangeable. The I′t values appear less susceptible to accidental errors. In some cases a discrepancy has been found between the rate of uptake of radioiodine during the 1st hr following the injection and the 24 hr uptake value, a low rate of uptake being accompanied by a 24 hr absolute uptake which was at least normal. This may be due to the mobilization of vaso-constrictor substances in the patient during the 1st hr. These anomalies occurred chiefly in patients suffering from some kind of anxiety neurosis.