STABILITY OF VALUES FOR THYROID RADIOIODINE UPTAKE

Chronological changes in values for thyroid radioiodine uptake measure ments (RIU) have been reported in the last four decades. These changes are attributed to geographical and chronological variations in dietar y iodine intake in the population. Fluctuations in normal values for R IU can affect the interpretation of these diagnostic tests in patients . Methods: During the last 16 yr, thyroid RIU measurements using I-123 were obtained in 671 euthyroid patients and 274 hyperthyroid patients , of which 233 patients had a diffuse goiter and 41 patients had a nod ular goiter. RIU was measured 24 hr after the oral administration of I -123, 3.7-7.4 MB9 (0.1-0.2 mCi) with no changes in technique during th is period. Values (mean +/- s.d.) for RIU were calculated for various groups of patients for each year. Combined data for 1979-83 and 1988-9 4 were compared. Differences between mean values for each year were de termined by a one-way ANOVA and a pairwise comparison. Results: For eu thyroid patients, there were no significant differences in the mean an d range of values from year to year. Additionally, there were no signi ficant differences between the combined values for the earlier years ( 1979-83) and the later years (1988-94) for hyperthyroid patients. Mino r statistical variations in the yearly values for the hyperthyroid pat ients were evident but not clinically important. Conclusion: Values fo r thyroid uptake of I-123 in euthyroid and hyperthyroid patients in Bo ston have remained stable for the last 16 yr.