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Comparison of Thyroid Hormones in Euthyroid Athyreotic Patients Treated with Levothyroxine and Euthyroid Healthy Subjects
Int J Thyroidol 2019;12(1):28-34
Published online May 30, 2019;  https://doi.org/10.11106/ijt.2019.12.1.28
© 2019 Korean Thyroid Association.

Min Ji Jeon1, Suk Hyun Lee2,3, Jong Jin Lee2, Min Kyu Han4, Hong-Kyu Kim5, Won Gu Kim1, Tae Yong Kim1, Won Bae Kim1, Young Kee Shong1 and Jin-Sook Ryu2

Departments of Internal Medicine1 and Nuclear Medicine2, Asan Medical Center, University of Ulsan College of Medicine, Division of Nuclear Medicine, Department of Radiology, Hallym University Kangnam Sacred Heart Hospital, Hallym University College of Medicine3, Departments of Clinical Epidemiology, Biostatistics4 and Health Promotion Center5, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
Correspondence to: Jin-Sook Ryu, MD, PhD, Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea
Tel: 82-2-3010-4593, Fax: 82-2-3010-4588, E-mail: jsryu2@amc.seoul.kr
Received April 23, 2019; Revised May 15, 2019; Accepted May 16, 2019.
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background and Objectives: Levothyroxine (L-T4) monotherapy to normalize TSH level might be not sufficient to restore serum free triiodothyronine (fT3) levels in hypothyroid patients. This study aimed to compare the thyroid hormone levels in euthyroid L-T4 treated athyreotic patients and euthyroid healthy control subjects. Materials and Methods: We included 69 euthyroid L-T4 treated athyreotic female patients after total thyroidectomy and radioactive iodine ablation therapy and 90 euthyroid healthy female. Serum fT3 and free thyroxine (fT4) levels were simultaneously measured using two different assay kits (A and B). Results: The serum fT4 level was higher in the athyreotic patients (kit A: p<0.001, kit B: p=0.046), and the serum fT3 level was higher in control subjects (kit A: p=0.047, kit B: p=0.102). In the control group, the serum fT3 level was stable and not correlated with the TSH level (kit A: tau=−0.10, p=0.18, kit B: tau=−0.06, p=0.40). However, in the patient group, the serum fT3 level was negatively correlated with the TSH level (kit A: tau=−0.22, p=0.012, kit B: tau=−0.31, p<0.001). All thyroid hormone parameters measured by kit A showed higher area under the curve values than those measured by kit B for distinguishing the patients from the control subjects. Conclusion: The serum fT3 levels in L-T4 treated athyreotic euthyroid patients were significantly lower than and varied from those of euthyroid healthy control subjects. Thus, L-T4 monotherapy might not be appropriate for some athyreotic patients to maintain optimal T3 levels.
Keywords : Thyroid hormones, Triiodothyronine, Thyroxine, Thyroidectomy