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Thyroid Function

Thyroid Function

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Thyroglobulin (Tg) is a storage form of the thyroid hormones produced by follicular cells of the thyroid, and is released into serum in conjunction with T3 and T4.

Thyroid physiology
Patterns of derangement
Suppressed TSH with Elevated T4
Consistent with primary hyperthyroidism
Suppressed TSH with Normal T4
Suggestive of subclinical hyperthyroidism if asymptomatic
Suppressed / Normal TSH with Reduced T4
Nonspecific, with several potential causes including central hypothyroidism
Elevated TSH with Reduced T4
Consistent with primary hypothyroidism
Elevated TSH with Normal T4
Suggestive of subclinical hypothyroidism if asymptomatic
Normal / Elevated TSH with Elevated T4
Nonspecific, with several potential causes including central hyperthyroidism
Clinical syndromes
Hyperthyroidism
Hypothyroidism
Nonthyroidal Illness

Thyroid Function

Summary of Interpretation
Thyroid Stimulating Hormone (TSH)
First line test for thyroid dysfunction
Free Thyroxine (T4)
Measure of non-protein bound thyroxine
Free Triiodothyronine (T3)
Rarely used in diagnosis of thyroid disease
Thyroglobulin
Rarely measured in clinical practice

Thyroid Antibodies

Anti-Thyroglobulin Antibodies
Present in Hashimoto's, though rarely required for diagnosis
Anti-TPO Antibodies
Present in Hashimoto's, though rarely required for diagnosis
Anti-TSH Receptor Antibodies
Pathognomonic of Grave's, though not always required for diagnosis

Thyroglobulin

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Overview

Thyroglobulin (Tg) is a storage form of the thyroid hormones produced by follicular cells of the thyroid, and is released into serum in conjunction with T3 and T4.
Thyroglobulin (Tg) is not routinely measured in clinical practice.
- Clinical Use of Thyroglobulin Testing
- Diagnosis of thyrotoxicosis factitia - used to distinguish surreptitious thyroxine ingestion from other causes of hyperthyroidism, as thyroglobulin will remain normal with exogenous thyroxine use
- Thyroid cancer - assessing for residual tumour post resection, or monitoring for recurrence

Last updated on October 17th, 2018

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Grounds D, Richmond V. Managing subclinical hypothyroidism. Australian Prescriber. 1999;22(6).

Halsall DJ, English E, Chatterjee VK. Interference from heterophilic antibodies in TSH assays. Annals of clinical biochemistry. 2009 Jul;46(4):345-6.

Kasagi K, Kousaka T, Higuchi K, Iida Y, Misaki T, Alam MS, Miyamoto S, Yamabe H, Konishi J. Clinical significance of measurements of antithyroid antibodies in the diagnosis of Hashimoto's thyroiditis: comparison with histological findings. Thyroid. 1996 Oct;6(5):445-50.

Koulouri O, Moran C, Halsall D, Chatterjee K, Gurnell M. Pitfalls in the measurement and interpretation of thyroid function tests. Best practice & research Clinical endocrinology & metabolism. 2013 Dec 1;27(6):745-62. Mortimer RH. Thyroid function tests. Australian Prescriber. 2011 Feb 1;34(1):12-5. Mullur R, Liu YY, Brent GA. Thyroid hormone regulation of metabolism. Physiological reviews. 2014 Apr;94(2):355-82.

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