Free T4 Index (T7)

Specialist

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BadLargely superseded by direct Free T4 measurement; rarely needed today.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

within Thyroid