Normal reference values for thyroid uptake of technetium-99m pertechnetate for the Namibian population

Abstract

Objective: Historically, changes in normal thyroid uptake values for iodine have been reported in different geographical areas. These changes have been linked to geographical and chronological fluctuations in dietary iodine intake in different populations. Namibia is a country with mixed ethnicity, with access to dietary iodine in table salt. Despite historical reports on deviating normal thyroid uptake values (emphasising the importance of establishing local normal reference values), the relevant Namibian authorities have never revised these reference values, nor have local reference values been established. The aim of this study was to establish the normal reference values for thyroid uptake of technetium-99m pertechnetate in the Namibian population. Design: Participants who were considered to be euthyroid completed a questionnaire designed to exclude individuals with thyroid pathologies, as well as those with renal or heart disease. Settings and subjects: The study cohort consisted of 76 participants (58 women and 18 men), ranging in age from 39-81 years. The participants were of mixed ethnicity, consisting of Hereros, Ovambos, Damaras, Namas, Coloureds, Caucasians and other (non-Namibian immigrants), and were from Windhoek, Namibia. Studies were performed at the Windhoek Central Hospital. Outcome measures: Blood was drawn for thyroid hormone assessment. Participants were then given 100 MBq of technetium-99m pertechnetate intravenously, and their percentage thyroid uptake recorded after 20 minutes. Results: In this study, thyroid-stimulating hormone, triiodothyronine, and thyroxine levels were found to be 1.7 μIU/ ml, 4.9 pmol/ml and 10.3 pmol/ml, respectively. Analysis of the empirical data showed that the normal reference uptake value for technetium-99m pertechnetate in the studied population ranged between 0.04% and 2.40%.The fifth and 95th percentiles for pertechnetate uptake were 0.15% and 1.69%, respectively. Conclusion: These results provide new evidence which supports the importance of periodical evaluation of normal thyroid uptake reference values for technetium-99m pertechnetate.