II. Indications

  1. Used to calculate Free Thyroxine Index (FTI)
    1. Interpret in conjunction with Total T4 or Total T3
    2. Corrects for abnormal Thyroid Binding Globulin (TBG)
  2. Free T4 also corrects for Thyroid Binding Globulin
    1. Free T4 is preferred over FTI (and T3RU)

III. Measurement

  1. Unbound Thyroid Binding Globulin filled with T3
  2. Remaining unbound Triiodothyronine (T3) is measured

IV. Interpretation: Increased T3 Resin Uptake

V. Interpretation: Decreased T3 Resin Uptake

  1. Hypothyroidism
  2. Pregnancy
  3. Hepatitis
  4. Porphyria
  5. X-Linked increased Thyroid Binding Globulin (TBG)
  6. Primary Biliary Cirrhosis
  7. Malnutrition
  8. Drugs
    1. Estrogen
    2. Oral Contraceptives
    3. Perphenazine
    4. Fluorouracil
    5. Clofibrate

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