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Thyroid Function

Free Triiodothyronine (T3)

April 28th, 2020


Free T3 is a measure of the triiodothyronine not bound to serum proteins such as thyroid-binding globulin, albumin or transthyretin.
    • Normal Range

    • 2.0 - 3.5 pg/mL
Measurement of free T3 is not generally required for the diagnosis of thyroid disease.
  • Pearls

  • Free T3 measurement is useful for diagnosing T3 thyrotoxicosis in patients with reduced TSH and normal T4.
  • Free T3 may be useful to confirm suspected hyperthyroidism, as it becomes elevated prior to T4.
  • Free T3 is not useful in the diagnosis of hypothyroidism as it is the last test to become abnormal in this setting.
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