The utility of technetium-99m pertechnetate thyroid scintigraphy assessing thyroid/salivary ratio as an alternative to thyroid uptake percentage in evaluation of thyroid function, with establishing normal reference values of both parameters: single Egyptian center study

Abstract

Background/Objective Management of thyroid disorders depends on accurate clinical assessment, appropriate investigations and radionuclide imaging, which plays an established important role either qualitatively or quantitatively. The aim of this study was to assess the utility of the thyroid/salivary ratio (TSR) as an alternative to technetium-99m (Tc99m) pertechnetate thyroid uptake (TcU) percentage in the evaluation of thyroid function and in the same time to establish reference range for the thyroid uptake of Tc99m-pertechnetate and TSR among Egyptian populations. Patients and methods This retrospective study enrolled 270 patients, out of which 250 with different thyroid disorders and 20 without thyroid diseases, as a control group who all underwent full clinical examination, thyroid function tests and Tc99m pertechnetate thyroid scintigraphy. The TcU percentage and TSR were calculated and then correlated to the thyroid hormonal profile. Results The normal reference ranges of TcU and TSR were 0.75–3.5% and 1.25–4.8%, respectively. The sensitivity and specificity of TSR to diagnose hyperthyroidism were slightly lower compared with TcU (84.5 and 92.3% vs. 86.2 and 98.3%, respectively) at TSR cutoff value of more than 4.8 and TcU cutoff value of more than 3.5. Meanwhile, they had comparable sensitivity and specificity to diagnose hypothyroidism (86.0 and 93.3% vs. 86.5 and 94.5%) at cutoff values <0.75 and <1.25, respectively. Conclusion The current study established a reference range for TcU and TSR in our institution. TSR is comparable to TcU in the evaluation of thyroid function among hyper-and hypothyroid patients and TSR can be used in doubtful cases of mal-thyroid function for confirmation of the diagnosis.