Thyroid related

Author: Nat Pernick, M.D. (see Authors page)

Revised: 23 February 2016, last major update March 2011

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Hyperthyroidism [title] chemistry
Cite this page: Hyperthyroidism. website. Accessed October 27th, 2016.
Definition / General
  • See also Hyperthyroidism in Thyroid chapter
  • Hyperfunction of gland (usually elevated levels of free T3 / T4, but see subclinical hyperthyroidism below)
  • Thyrotoxicosis refers to clinical effects of free thyroid hormone
  • Source may not be thyroid gland
  • May be masked by nonthyroidal illness syndrome (J R Soc Med 2003;96:185)
  • Graves disease (85%-circulating autoantibodies to TSH receptor)
  • Overdose of exogenous thyroid hormone, hyperfunctioning multinodular goiter or thyroid adenoma, thyroiditis, struma ovarii, iodide ingestion, choriocarcinoma/hydatidiform mole, maternal Graves disease, pituitary adenoma
  • High free T4
    • TSH may be low (primary hyperthyroidism) or high (secondary hyperthyroidism)
  • In subclinical hyperthyroidism, T3 and T4 are normal but TSH is low
Primary hyperthyroidism
  • Intrinsic thyroid gland abnormality producing excess T4
  • High free T4, low TSH, normal TRH stimulation test

Secondary hyperthyroidism
  • Abnormal TRH stimulation test (problem is at level of pituitary, including TSH producing tumors), high TSH, high free T4

Subclinical hyperthyroidism

T3 hyperthyroidism
  • 1 - 4% of hyperthyroid patients
  • Low TSH, high free T3, normal free T4
  • Associated with early treatment of hyperthyroidism with antithyroid drugs

T4 hyperthyroidism
  • Beta blockers for symptoms, thionamide-type drugs to block new hormone synthesis, iodine to block release of T4/T3