Ann Lab Med.  2019 Jan;39(1):3-14. 10.3343/alm.2019.39.1.3.

Laboratory Testing in Thyroid Conditions - Pitfalls and Clinical Utility

• Soh SB
• Aw TC

• KMID: 2420265
• DOI: http://doi.org/10.3343/alm.2019.39.1.3

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.

Keyword

Thyroid function test; Thyroid-stimulating hormone; Free thyroxine; Free triiodothyronine; Thyroglobulin; Thyroglobulin antibodies; Thyroid peroxidase antibodies; Thyroid-stimulating hormone receptor antibodies; Calcitonin

MeSH Terms

Antibodies
Biomarkers, Tumor
Calcitonin
Critical Illness
Diagnosis
Graves Disease
Hematologic Tests
Iodide Peroxidase
Physiology
Pregnancy
Receptors, Thyrotropin
Thyroglobulin
Thyroid Function Tests
Thyroid Gland*
Thyroid Neoplasms
Thyroiditis
Thyrotropin
Thyroxine
Triiodothyronine
Antibodies
Biomarkers, Tumor
Calcitonin
Iodide Peroxidase
Receptors, Thyrotropin
Thyroglobulin
Thyrotropin
Thyroxine
Triiodothyronine

Figure

• 

  Fig. 1 Algorithm for the interpretation of thyroid function test results.Abbreviations: TSH, thyroid-stimulating hormone; Free T4 (FT4), free thyroxine.

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