Assessment of Thyroid Uptake Ratio Values in a Normal Population. Establishment of Normal Reference Values for 99mTc-Pertechnetate Thyroid Uptake in an Australian Population.

Abstract

Introduction: Thyroid scintigraphy with ^99mTc-pertechnetate is a nuclear medicine examination performed since the early 1970s that allows for functional assessment of the thyroid. Quantitative thyroid uptake expressed as a percentage of the injected dose is calculated in many centres as part of the examination. Our current normal institutional reference of 1%-4% was derived from a 1971 study. Uptake values may change with geographical location and over time, with international studies reporting updated normal reference values for local populations of 0.2%-2.0%, 0.2%-2.0%, 0.26%-1.64% and 0.4%-2.4%. To our knowledge, there have been no published reports on normal reference values for Australian populations. The aim of this study was to establish normal reference values for ^99mTc-pertechnetate thyroid uptake in a Victorian, Australian patient population.

Methods: A retrospective audit and prospective study of 271 consecutive patients undergoing parathyroid scans was performed between January 2017 and December 2021. Anterior thyroid images acquired following intravenous injection of ^99mTc-pertechnetate were reviewed to calculate thyroid uptake. Patients with thyroid conditions, abnormal biochemical thyroid function tests and/or abnormal appearances on ^99mTc-pertechnetate thyroid scans were excluded.

Results: Of the 271 patients, 151 studies met the eligibility criteria and were included for analysis. The median thyroid uptake value was 0.97% with a 95% reference range of 0.4%-2.4%.

Conclusion: This study established a thyroid uptake reference range of 0.4%-2.4% using ^99mTc-pertechnetate, which was lower than the values used in our institution. Highlighting the need for periodic evaluation of normal uptake values.