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Interpretation of Thyroid Function Test

  • March 22,2021
  • 5 Min Read
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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