Thyroid hormones thyroxine (T4) and tri-iodothyronine (T3) are produced, stored, and secreted by the thyroid gland. These hormones, particularly T3, play a major role in multiple biological and metabolic processes. They act by binding to thyroid receptors that are distributed in almost every organ. Typically, this process regulates gene transcription and the subsequent production of various proteins that are involved in development, growth, and cellular metabolism.  Thyroid function tests (TFTs) are the most commonly used endocrine test.
Northeast Florida Endocrine & Diabetes Associates
MS-A declares that she is a speaker for Novo Nordisk and Janssen.
Dr Mae Sheikh-Ali would like to gratefully acknowledge Dr Harshit Shah, Dr Melanie Thomas, Dr Anna Szafran-Swietlik, Dr Sandra Mesliniene, Dr Emad Naem, and Dr Abdul-Razzak Alamir, previous contributors to this monograph. HS, MT, AS-S, SM, EN, and A-RA declare that they have no competing interests.
Professor of Surgery
Virginia Commonwealth University
RM declares that he has no competing interests.
Professor of Medicine and Endocrinology
Medical Center Spijkenisse
Professor of Endocrinology
Royal Victoria Infirmary
Newcastle upon Tyne
SP declares that he has no competing interests.
Clinical Associate Professor of Medicine
Uniformed Services University of the Health Sciences
MA and Senior Medical Advisor
VSS declares that he has no competing interests.
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