Interpreting thyroid function tests and thyroid antibodies
Read TSH first, then free T4 and T3, sort the result into one of six patterns, know the assay traps (biotin, heterophile antibodies, non-thyroidal illness, drugs), and use TPO, Tg and TSH-receptor antibodies, plus the diabetes and adrenal autoantibodies, for the questions they actually answer.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- TSH first. It is the most sensitive marker of primary thyroid disease because of its log-linear relationship with free T4. The RCPA and the Australian algorithm advise TSH alone, with free T4 added by the laboratory if TSH is abnormal.
- TSH misleads in central disease, unstable states and assay interference. In those, read free T4 first.
- Sort every result into one of six patterns (table below). Most "odd" results are interference, drugs, non-thyroidal illness or timing.
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Sources
- Thyroid function testing for adult diagnosis and monitoring (position statement)AU/NZRoyal College of Pathologists of Australasia, 2017 (no newer RCPA statement found when checked November 2026)
- Adult thyroid disorder testing algorithmAU/NZNPS MedicineWise (now Australian Commission on Safety and Quality in Health Care), v3
- 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosisAmerican Thyroid Association (Ross DS et al., Thyroid 2016;26:1343-421), 2016 (still the current general ATA thyrotoxicosis guideline, checked November 2026)
- American Thyroid Association 2026 guidelines for thyroid disease in preconception, pregnancy, and postpartumAmerican Thyroid Association (Thyroid 2026;36(5):481-544), 2026 (replaces the 2017 pregnancy guideline)
- Standards of Care in Diabetes 2026: Section 2, Diagnosis and classification of diabetesAmerican Diabetes Association (Diabetes Care 2026;49(Suppl 1)), 2026
- Bartalena L, Bogazzi F, Chiovato L et al. 2018 European Thyroid Association (ETA) guidelines for the management of amiodarone-associated thyroid dysfunction. Eur Thyroid J 2018;7(2):55-66European Thyroid Association, 2018
- Endocrinology (Therapeutic Guidelines)AU/NZTherapeutic Guidelines Ltd
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Deploy to Cloudflare on push to main