The FTI is a normalized determination that remains relatively constant in healthy individuals and compensates for abnormal levels of binding proteins.
What did it measure?
- The FTI is determined by the following calculation: FTI = Total T4 x (%T-Uptake/100)
Why was it ordered?
- Rough estimate of the unbound fraction of T4
- Hyperthyroidism causes increased FTI
- Hypothyroidism causes decreased FTI
What has replaced it?
- FTI has been replaced with FT4 assays
