Interpretation of Thyroid Function Test

FT3/FT4↑ TSH↓*	Graves’ disease Toxic multinodular goiter Toxic adenoma Thyroiditis (post-viral, post-partum) Iodine deficiency or excess Excess Iodine intake Excess thyroxine ingestion Pregnancy-related (hyperemesis gravidarum; hydatidiform mole) Congenital hyperthyroidism
FT3/FT4↓ TSH↔ /↓*	Non-thyroidal illness Central hypothyroidism Isolated TSH deficiency Assay interference
FT3/FT4↑ TSH↔ /↑	Assay interference Thyroxine replacement therapy Drugs (eg: amiodarone, heparin) Non-thyroidal illness Neonatal period TSH – secreting pituitary adenoma Resistance to thyroid hormone, transportation or metabolism
FT3/FT4↓ TSH↔ /↑	Autoimmune thyroiditis (Hashimoto’s; atrophic) Post-radioiodine therapy/ thyroidectomy Hypothyroid phase of thyroiditis Drugs (amiodarone, lithium, TKIs, ATDs) Iodine deficiency or excess Neck infection Reidel’s thyroiditis Thyroid infiltration (tumour, amyloid) Congenital hypothyroidism
FT3/FT4↔ TSH↑	Subclinical hyperthyroidism Poor compliance with thyroxine Malabsorption of thyroxine Drugs (amiodarone) Assay interference Non-thyroidal illness recovery TSH resistance
FT3/FT4↔ TSH↓*	Subclinical hyperthyroidism Recent treatment for hyperthyroidism Drugs (eg: steroids, dopamine) Assay interference Non-thyroidal illness

FT3– Free Triiodothyronine; FT4 – Free Thyroxine; TSH – Thyroid Stimulating Hormone

Reference:

Koulouri O, Moran C, Halsall D, Chatterjee K, Gumell M. Pitfalls in the measurement and interpretation of thyroid function tests. Best Pract Res Clin Endocrinol Metab. 2013 Dec; 27(6):745-62.

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