Thyroid disorders

Last updated: June 18, 2021

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This article provides an overview of the most common thyroid disorders (hypothyroidism and hyperthyroidism) and thyroid function testing.

For more information on specific conditions, see the articles on “Hypothyroidism,” "Hyperthyroidism and thyrotoxicosis,” “Thyroid nodules,” and “Thyroid cancer.”

Overview of clinical features in thyroid-related disorders
Hypothyroidism Hyperthyroidism
  • Hoarse voice, difficulty articulating words
  • Tremulous voice
  • Cold intolerance
  • Fatigue, decreased physical activity
  • Weight gain (despite decreased appetite)
  • Heat intolerance
  • Weakness, fatigue
  • Weight loss (despite increased appetite)
  • Frequent bowel movements (due to intestinal hypermotility)

For further information, see “Hypothyroidism” and "Hyperthyroidism and thyrotoxicosis.”

Overview of thyroid function tests in thyroid disorders
Etiology Thyroid function tests
TSH level Free T4 Free T3
Overt hypothyroidism Primary hypothyroidism
Secondary hypothyroidism
Tertiary hypothyroidism
Subclinical hypothyroidism
  • Mildly ↑
  • Normal
Euthyroid sick syndrome Low T3 syndrome
  • Occurs in severe illness or severe physical stress (most common in intensive care patients)
  • Normal
  • Normal
Low T3 low T4 syndrome
Primary hyperthyroidism
Secondary hyperthyroidism
  • Normal/↑
Subclinical hyperthyroidism
  • Normal

For further information, see “Diagnostics” in “Hypothyroidism” and “Overview” in "Hyperthyroidism and thyrotoxicosis.”

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