Thyroid function testing

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Last reviewed: 21 Oct 2024

Last updated: 02 Apr 2024

Thyroid function tests (TFTs) are the most commonly used endocrine test. American Thyroid Association: thyroid function tests Opens in new window Thyroid hormones thyroxine (T4) and triiodothyronine (T3) are produced, stored, and secreted by the thyroid gland. These hormones, particularly T3, play a major role in multiple biologic 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.[1] This topic discusses indications for TFTs and the interpretation of results, in particular serum thyrotropin (TSH) levels and associated free T3 and free T4 levels.

Details

Thyroid hormone production
Thyroid hormone-binding proteins
Indications for TFTs: general considerations
Known thyroid dysfunction and preconception
Screening for thyroid dysfunction during pregnancy
Screening for congenital hypothyroidism
TFTs
Low TSH - associated with a high FT4 and/or FT3
Low TSH - associated with a low FT4 and/or FT3
Low TSH - associated with a normal FT4 and/or FT3
High TSH - associated with a high FT4 and/or FT3
High TSH - associated with a low FT4 and/or FT3
High TSH - associated with a normal FT4 and/or FT3
Normal TSH - associated with a low FT4 and/or FT3
Drug effects

Full details

Contributors

Authors

Joel Ehrenkranz, MD

Associate Professor

Division of Chemistry and Chemical Engineering

California Institute of Technology

Pasadena

Disclosures

JE declares that he has served on a writing group for the American Thyroid Association which drafted an article on thyroid function testing and was submitted for publication to the journal Thyroid.

Acknowledgements

Dr Joel Ehrenkranz would like to gratefully acknowledge Dr Mae Sheikh-Ali, 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 topic. HS, MT, AS-S, SM, EN, and A-RA declare that they have no competing interests. MS-A declares she is a speaker for IBSA and AbbVie. Both have brand names for levothyroxine (LT4) medication.

Peer reviewers

Ronald Merrell, MD

Professor of Surgery

Virginia Commonwealth University

Richmond

Disclosures

RM declares that he has no competing interests.

Georg Hennemann, MD

Professor of Medicine and Endocrinology

Medical Center Spijkenisse

The Hague

The Netherlands

Disclosures

Not disclosed.

Simon Pearce, MD

Professor of Endocrinology

Newcastle University

Endocrine Unit

Royal Victoria Infirmary

Newcastle upon Tyne

Disclosures

SP declares that he has no competing interests.

V.S. Schneider, MD

Clinical Associate Professor of Medicine

Uniformed Services University of the Health Sciences

Bethesda

MA and Senior Medical Advisor

NASA Headquarters

Washington

Disclosures

VSS declares that he has no competing interests.

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Thyroid function testing

Summary

Details

Contributors

Authors

Joel Ehrenkranz, MD

Disclosures

Acknowledgements

Peer reviewers

Ronald Merrell, MD

Disclosures

Georg Hennemann, MD

Disclosures

Simon Pearce, MD

Disclosures

V.S. Schneider, MD

Disclosures

Patient information

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