Ann Lab Med 2019; 39(1): 3-14  https://doi.org/10.3343/alm.2019.39.1.3
Laboratory Testing in Thyroid Conditions – Pitfalls and Clinical Utility
Shui-Boon Soh, MRCP (UK)1,2 and Tar-Choon Aw, FRCPA2,3
1Department of Endocrinology, Changi General Hospital, Singapore; 2Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; 3Department of Laboratory Medicine, Changi General Hospital, Singapore
Corresponding author: Tar-Choon Aw, FRCPA
https://orcid.org/0000-0002-7814-8836
Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, Singapore 529889, Singapore
Tel: +65-6850-4927
Fax: +65-6426-9507
E-mail: tarchoon@gmail.com
Received: April 21, 2018; Revised: May 29, 2018; Accepted: September 2, 2018; Published online: January 1, 2019.
© Korean Society for Laboratory Medicine. All rights reserved.

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
Thyroid disorders are common, affecting more than 10% of people in the US, and laboratory tests are integral in the management of these conditions. The repertoire of thyroid tests includes blood tests for thyroid-stimulating hormone (TSH), free thyroxine, free triiodothyronine, thyroglobulin (Tg), thyroglobulin antibodies (Tg-Ab), thyroid peroxidase antibodies (TPO-Ab), TSH receptor antibodies (TRAb), and calcitonin. TSH and free thyroid hormone tests are frequently used to assess the functional status of the thyroid. TPO-Ab and TRAb tests are used to diagnose Hashimoto’s thyroiditis and Graves’ disease, respectively. Tg and calcitonin are important tumor markers used in the management of differentiated thyroid carcinoma and medullary thyroid carcinoma (MTC), respectively. Procalcitonin may replace calcitonin as a biomarker for MTC. Apart from understanding normal thyroid physiology, it is important to be familiar with the possible pitfalls and caveats in the use of these tests so that they can be interpreted properly and accurately. When results are discordant, clinicians and laboratorians should be mindful of possible assay interferences and/or the effects of concurrent medications. In addition, thyroid function may appear abnormal in the absence of actual thyroid dysfunction during pregnancy and in critical illness. Hence, it is important to consider the clinical context when interpreting results. This review aims to describe the above-mentioned blood tests used in the diagnosis and management of thyroid disorders, as well as the pitfalls in their interpretation. With due knowledge and care, clinicians and laboratorians will be able to fully appreciate the clinical utility of these important laboratory tests.
Keywords: Thyroid function test, Thyroid-stimulating hormone, Free thyroxine, Free triiodothyronine, Thyroglobulin, Thyroglobulin antibodies, Thyroid peroxidase antibodies, Thyroid-stimulating hormone receptor antibodies, Calcitonin



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