Chemistry, toxicology & urinalysis

Organ specific


Hyperthyroidism-lab diagnosis

Topic Completed: 1 March 2011

Minor changes: 29 September 2021

Copyright: 2002-2021,, Inc.

PubMed Search: Hyperthyroidism [title] chemistry

Nat Pernick, M.D.
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Cite this page: Pernick N. Hyperthyroidism-lab diagnosis. website. Accessed December 3rd, 2021.
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
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