Lab

Free Thyroxine Index

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Free Thyroxine Index, Free T4 Index, FTI, FT4I

  • Interpretation
  • Normal
  1. Free Thyroxine Index: 4-11
  • Indications
  1. Largely replaced by Free T4 (Free Thyroxine)
  2. Corrects for abnormal Thyroid Binding Globulin (TBG)
  3. Free T4 also corrects for Thyroid Binding Globulin
    1. Free T4 is preferred over FTI
  • Measurement
  1. Calculated: T4 x T3 Binding Ratio (T3RU)