Lab

Triiodothyronine

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Triiodothyronine, T3, Free T3

  • 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