This chapter explains normal thyroid function and provides an overview of thyroid disorders, including: hypothyroidism, hyperthyroidism, goiter, thyroiditis, Hashimoto’s thyroiditis and Graves’ disease. For each analyte used in the thyroid field the biological function is explained, with the clinical applications of the test and its limitations. Typical assay technology is described. The type of sample and frequency of use are included, with an example reference interval (for background information only). The analytes included are: thyrotropin (TSH), thyroxine (T₄), free T₄, triiodothyronine (T₃), free T₃, thyrotropin receptor antibodies, thyroid peroxidase antibodies, thyroglobulin antibodies and thyroglobulin. In the final part of the chapter, thyroid testing strategies are reviewed with an example testing algorithm and summaries of the clinical features of hypothyroidism and hyperthyroidism. There is a section on the limitation of using TSH measurement as the sole screening method and a table of analyte classifications (low, low normal, normal, slightly raised and raised) for a wide range of thyroid disorders.

Rhys John was a Clinical Biochemist at the Department of Medical Biochemistry at the University Hospital of Wales, Cardiff. Among his roles were Consultant Clinical Biochemist, Deputy Head of Department, Director of the Supraregional Assay Service Endocrine Laboratory, Director of the Neural Tube Defect screening service, Director of the Down’s Syndrome screening service, Director of the Congenital Hypothyroid screening service and Honorary Senior Lecturer in the University of Cardiff, College of Medicine. He held locum posts at the Riyadh Armed Forces Hospital, the Taif Maternity Hospital, Saudi Arabia and at hospitals in the UK. Research interests have included the development of immunoassays for the investigation of thyroid dysfunction, and in the clinical aspects of thyroid disease. Publication of research has resulted in over 100 scientific papers and co-author of various book chapters. Awards have included a Sir Winston Churchill Travelling Fellowship and a World Health Organization Fellowship.

Nic Christofides. Having worked in academia for 11 years (at the Imperial with Sir Stephen Bloom) and 22 years in industry (Ortho Clinical Diagnostics Scientific) Nic is currently working as a scientific consultant. This entails advising customers (small and large companies) on all aspects of immunoassay development, including R&D, validation, trouble-shooting and helping with promotional materials, e.g. publications.

This chapter also contains material contributed to previous editions by Carole A. Spencer and David Wild.

Thyroid, iodine, euthyroid, hypothyroidism, hyperthyroidism, goiter, thyroiditis, Hashimoto’s thyroiditis, Graves’ disease, T₃-toxicosis, T₄-toxicosis, non-thyroidal illness, familial dysalbuminemic hyperthyroxinemia, thyroxine (T₄), triiodothyronine (T₃), thyrotropin, free T₄, free T₃, thyroglobulin, thyrotropin receptor antibodies, thyroid peroxidase antibodies, thyroglobulin antibodies.

Reiners, C. Thyroid Cancer in 2013: Advances in our understanding of differentiated thyroid cancer. Nat. Rev. Endocrinol. 10, 69–70 (2014).

Bartalena, L. Diagnosis and management of Graves Disease: a global overview. Nat. Rev. Endocrinol. 9, 724–734 (2013)

An alternative thyroid testing algorithm is available at www.arupconsult.com. Select "Algorithms".