Changes in the normal range of thyroidal radioiodine uptake

Three series of patients shown to be euthyroid but originally referred for thyroid uptake tests in vivo have been compared. In 1958-59, the ;normal' mean thyroid uptake was 23.5% and 38.2% respectively at four and 24 hours. By 1967, the mean uptakes had dropped to 20.4% and 31.6%-a significant change at both times. By 1972 there was, however, no sign of a further reduction of the mean normal values for thyroid uptake. These results are compared with changes observed in other series in the USA and elsewhere.