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BadLargely superseded by direct Free T4 measurement; rarely needed today.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.
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