Assessment of normal reference values for thyroid uptake of technetium-99m pertechnetate in a Saudi population

BACKGROUND: Thyrotoxicosis is a common medical problem. Thyroid nuclear imaging with either I(123) or technetium-99m (Tc-99m) pertechnetate are used to determine the cause. Although I(123) has been the standard technique, Tc-99m pertechnetate is now commonly used, acceptable and easier to perform. The commonly used normal value of Tc-99m pertechnetate is 1–4%, but lower normal values have been reported in different populations. OBJECTIVE: Determine normal reference range of Tc-99m pertechne-tate thyroid uptake for thyroid scintigraphy in Saudi Arabia. DESIGN: Retrospective, cross-sectional. SETTING: Nuclear medicine service at tertiary care center in Riyadh. PATIENTS AND METHODS: We used data from biochemically euthyroid patients who underwent a thyroid Tc-99m pertechnetate scan while having parathyroid scintigraphy for hyperparathyroidism between April 2009 to April 2019. Medical records and biochemical thyroid function tests were reviewed and Tc-99m pertechnetate thyroid uptake values were determined for each patient. MAIN OUTCOME MEASURES: Thyroid uptake of Tc-99m pertechne-tate in euthyroid patients. SAMPLE SIZE: 167 RESULTS: The mean and median uptake of Tc-99m pertechnetate in euthyroid patients were 0.86% and 1.0%, respectively, and the inter-quartile range was 0.0–1.0%. The normal reference range in the study population was 0.2-2%. Thyroid uptake inversely correlated with age in females (r=−0.37, P<.001), males (r=−0.46, P=.001), and for all patients (r=?0.39, P<.0001). CONCLUSION: The range for normal thyroid Tc-99m pertechnetate was lower than the standard 1-4% range. Moreover, uptake decreased with age. Further studies are needed to establish the normal age-adjusted uptake for the thyroid Tc-99m pertechnetate scan. LIMITATIONS: Single center and retrospective. CONFLICT OF INTEREST: None.