← Blood tests
Free T4 Index (T7)
Specialistalso fti
What it isA legacy calculation combining total T4 with T3 uptake to estimate free T4 indirectly before direct free T4 assays existed.
DoesProvides a back-calculated estimate of biologically available T4.
GoodA mid-range FTI tracks normal free T4.
BadLargely superseded by direct Free T4 measurement; rarely needed today.
- Standard
- 4.6–10.9.
- Optimal
- 6.5–8.5 (narrow target)
- Modifiers
- Same as Total T4.
How to optimize
- Lifestyle
- Same as Free T4.
- Diet
- Same as Free T4.
- Supplements
- Same as Free T4.
- Peptides
- —
- Drugs
- Levothyroxine.
Reference ranges are general adult lab norms; optimal ranges are editorial picks from the longevity literature — not medical advice. Always interpret results with your physician.
within Thyroid