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[Change of 99m technetium-pertechnetate uptake by the thyroid under suppression (TcTus) induced by optimization of
M J Reinhardt1, T Trupkovic, T Schumacher
1Abteilung Nuklearmedizin, Klinikum der Albert-Ludwigs-Universität, Freiburg i. Br., Deutschland. reinhami@ukl.uni-freiburg.de
Aim:
The present study deals with the change of the 99mTechnetium-pertechnetate thyroid uptake under suppression (TcTUs) in dependence on the urinary iodine excretion.
Methods:
The study collective comprises 510 patients with euthyroid goiter (N = 91), with functional thyroid autonomy (N = 361) and with Graves, disease (N = 58), who were examined in the own thyroid ambulance between January 1995 and February 1997 and who presented with endogeneous or exogeneous TSH suppression. All patients received a quantitative thyroid scintigraphy with 99mTechnetium-pertechnetate and a measurement of the urinary iodine excretion.
Results:
The TcTUs from the whole collective shows an inverse correlation to the urinary iodine excretion for the range of 0 to 500 micrograms iodine/g creatinine. The TcTUs remains constant on a low basal level for iodine excretion values over 500 micrograms iodine/g creatinine. Significant differences occur in dependence on the underlying disease. TcTUs is constantly low in patients with euthyroid goiter, independent of the iodine excretion value. The TcTUs is significantly increased in patients with functional thyroid autonomy or Graves' disease when iodine excretion is below 100 or 50 micrograms iodine/g creatinine respectively, but shows only minor changes when iodine excretion rises up to 500 micrograms iodine/g creatinine. When iodine excretion exceeds 500 micrograms iodine/g creatinine, the TcTUs of patients with thyroid autonomy drops down to a low basal level.
Conclusion:
The reference range of TcTUs for assessing functional thyroid autonomy will not change significantly when the iodine supply in Germany improves. The TcTUs of patients with functional thyroid autonomy might be up to one third higher under conditions of iodine deficiency than in iodine sufficiency. This should be taken into account, when therapeutical consequences were derived from the TcTUs. The TcTUs cannot be interpreted for iodine excretion values over 500 micrograms iodine/g creatinine.