Stability of values for thyroid radioiodine uptake

Chronological changes in values for thyroid radioiodine uptake measurements (RIU) have been reported in the last four decades. These changes are attributed to geographical and chronological variations in dietary iodine intake in the population. Fluctuations in normal values for RIU can affect the interpretation of these diagnostic tests in patients.

During the last 16 yr, thyroid RIU measurements using 123I were obtained in 671 euthyroid patients and 274 hyperthyroid patients, of which 233 patients had a diffuse goiter and 41 patients had a nodular goiter. RIU was measured 24 hr after the oral administration of 123I, 3.7-7.4 MBq (0.1-0.2 mCi) with no changes in technique during this period. Values (mean +/- s.d.) for RIU were calculated for various groups of patients for each year. Combined data for 1979-83 and 1988-94 were compared. Differences between mean values for each year were determined by a one-way ANOVA and pairwise comparison.

For euthyroid patients, there were no significant differences in the mean and range of values from year to year. Additionally, there were no significant differences between the combined values for the earlier years (1979-83) and the later years (1988-94) for hyperthyroid patients. Minor statistical variations in the yearly values for the hyperthyroid patients were evident but not clinically important.

Values for thyroid uptake of 123I in euthyroid and hyperthyroid patients in Boston have remained stable for the last 16 yr.