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Risk Factors for Indeterminate Response After Radioactive Iodine Therapy in Patients With Differentiated Thyroid Cancer

Jeong, Eugene MD*; Yoon, Joon-Kee MD, PhD*; Lee, Su Jin MD, PhD*; Soh, Euy Young MD, PhD; Lee, Jeonghun MD; An, Young-Sil MD, PhD*

doi: 10.1097/RLU.0000000000002653
Original Articles

Purpose We investigated the risk factors of indeterminate response (IDR) in patients who underwent recombinant human thyroid-stimulating hormone (rhTSH)–aided radioactive iodine therapy (RAIT).

Methods A total of 128 patients with papillary thyroid cancer were included in this retrospective study. The patients were classified into excellent response and IDR groups based on follow-up diagnostic whole-body scintigraphy (WBS) and TSH-stimulated thyroglobulin (Tg). Indeterminate response was defined as the presence of a faint uptake in the thyroid bed on the diagnostic WBS or a TSH-stimulated Tg detectable, but less than 10 ng/mL. Parameters that act as significant risk factors for IDR, including age, sex, stage, surgeon, time interval between surgery and RAIT, post-treatment WBS finding, urine iodine-to-creatinine ratio, TSH-unstimulated Tg, and rhTSH-stimulated Tg, were analyzed using a Cox proportional hazards regression method.

Results After treatment, 64 patients showed IDR. Recombinant human TSH–stimulated Tg was the only independent risk factor for predicting IDR. Patients with an rhTSH-stimulated Tg greater than 2 ng/mL prior to RAIT were 3.75 times more likely (95% confidence interval, 1.61–8.72) to have an IDR than those with a lower rhTSH-stimulated Tg (≤2 ng/mL).

Conclusions Pre-RAIT TSH-stimulated Tg levels are a risk factor for IDR after RAIT.

From the Departments of *Nuclear Medicine and Molecular Imaging

Surgery, Ajou University School of Medicine, Suwon, Korea.

Received for publication March 18, 2019; revision accepted April 23, 2019.

Conflicts of interest and sources of funding: none declared.

Correspondence to: Young-Sil An, MD, PhD, Department of Nuclear Medicine and Molecular Imaging, Ajou University School of Medicine, Worldcup-ro 164, Yongtong-gu, Suwon, Gyeonggi-do 16499, South Korea. E-mail:

Online date: June 3, 2019

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