Improving Thyrotoxicosis Diagnosis: The Clinical Necessity of Refining Tc-99m Pertechnetate Uptake Reference Ranges

Objectives: Accurate thyroid uptake assessment using Technetium-99m (Tc-99m) pertechnetate is essential for diagnosing thyrotoxicosis. This study evaluates the applicability of the current regional reference range (0.2%–2.0%) in Kuwait and investigates whether a refined range enhances diagnostic accuracy by reducing missed thyrotoxic cases. Material and Methods: A retrospective study was conducted on 218 thyrotoxic patients who underwent Tc-99m pertechnetate and 131I thyroid uptake studies at a tertiary hospital between 2018 and 2024. Patients with prior thyroid surgery, iodinated contrast exposure, or interfering medications were excluded. Statistical analyses, including quartile distribution and receiver operating characteristic (ROC) curve assessment, were used to determine a more precise diagnostic threshold. Results: Among 218 thyrotoxic patients, 56 (26%) had Tc-99m pertechnetate uptake (TU) within the current normal range, potentially leading to misdiagnosis. Refining the reference range to 0.5%–1.5% significantly reduced the number of missed thyrotoxic cases to 31 (14%). ROC analysis identified 0.5% as the optimal lower threshold, maximizing sensitivity (95.1%). The revised upper threshold of 1.5% improved the differentiation between normal and hyperfunctioning thyroid states, allowing better exclusion of non-hyperthyroid cases while maintaining high sensitivity. This refined range improved diagnostic accuracy, ensuring a more precise classification of thyrotoxic patients. Conclusion: The existing TU reference range may lead to underdiagnosis of thyrotoxicosis. A revised range of 0.5%–1.5% enhances diagnostic precision by optimizing sensitivity and specificity, ensuring more accurate identification of hyperthyroid cases. This adjustment has significant implications for thyroid imaging protocols and clinical decision-making.