Lab

Triiodothyronine

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Triiodothyronine, T3, Free T3, T3 Hormone

  • See Also
  1. Triiodothyronine Replacement
  2. Thyroid Function Test
  3. Thyroid Function Summary
  4. Thyroid Anatomy
  5. Thyroxine (Free T4)
  6. Thyroid Stimulating Hormone (TSH)
  7. Free Thyroxine Index (Free T4 Index)
  8. Thyroxine Binding Globulin (TBG)
  9. Thyroid Releasing Hormone (TRH)
  10. Antithyroid Antibody
  11. Thyroxine Replacement
  12. Hypothyroidism
  13. Hyperthyroidism
  14. Hypothyroidism in Pregnancy
  15. Thyroid Dysfunction in Pregnancy
  • Physiology
  1. See Thyroid Anatomy
  2. Images
    1. thyroidHormoneSynthesis.png
  • Interpretation
  • Normal Levels
  1. Triiodothyronine (T3): 80-180 ng/dl
  2. Free T3: 230-619 pg/dl
  • Mechanism
  • Measurement
  1. T3 radioimmunoassay measures bound and Free T3
    1. Affected by TBG levels as well as other factors
  2. Free Triiodothyronine (Free T3) measures only active T3
    1. Not affected by Thyroid Binding Globulin (TBG)
    2. Represents 0.3% of total T3
  3. False Hypothyroidism if impaired T4 to T3 conversion
    1. Systemic illness
    2. Fasting
    3. Surgical stress
    4. Drugs
      1. Prednisone
      2. Propylthiouracil
      3. Amiodarone
      4. Radiopaque contrast
      5. Propranolol