Chemistry, toxicology & urinalysis
Organ specific

Topic Completed: 1 March 2011

Minor changes: 2 April 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Hypothyroidism [title] thyroid

Nat Pernick, M.D.
Page views in 2019: 423
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Cite this page: Pernick N. Hypothyroidism. website. Accessed August 11th, 2020.
Definition / general
  • See also Hypothyroidism in Thyroid chapter
  • May initially have transient hyperthyroidism
  • May cause macrocytic, nonmegaloblastic anemia with normal RDW
Primary hypothyroidism
  • Due to:
    • Destruction or ablation of thyroid gland (surgery, radiation, Hashimoto thyroiditis, developmental)
    • Interference with thyroid hormone synthesis (idiopathic, genetic J Med Genet 2005;42:379)
    • Drugs (lithium, iodide, methimazole, PTU)
    • Iodine ingestion (Intern Med 2007;46:391) or iodine deficiency
  • T4 is low causing high TSH
  • Other causes:

Secondary hypothyroidism
  • Pituitary disorder causes reduced TSH secretion

Tertiary disease
  • Hypothalamic lesion causes reduced TRF secretion

Subclinical hypothyroidism

  • Hypothyroidism developing during infancy/childhood
  • May be due to maternal hypothyroidism (maternal T3/T4 crosses placenta and is critical to fetal brain development before fetal thyroid gland develops)
  • Now rare due to newborn testing and iodine supplementation (Pediatrics 2006;117:2290)

  • Chronic hypothyroidism in older child or adult
Additional references
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