Free Thyroxine Index (FTI / T7)
Free Thyroxine Index (FTI / T7) - a deterministic tool in Sophie Well's Clinical Math & Conversions group.
Open the Free Thyroxine Index (FTI / T7) → Runs in your browser. No signup, no tracking.
What this is
Free Thyroxine Index (FTI / T7) is one of 230 deterministic tools in Sophie Well's Clinical Math & Conversions group. Free Thyroxine Index (FTI / T7) - a deterministic tool in Sophie Well's Clinical Math & Conversions group.
When to use it
Use this tool when you need a quick, citable reference. Every calculation runs entirely in your browser - no inputs leave your device, no account is required, no AI is involved. The site enforces a strict Content Security Policy and ships no analytics or third-party CDN.
References
Clark F, Horn DB. Assessment of thyroid function by the combined use of the serum protein-bound iodine and resin uptake of 131-I-triiodothyronine. J Clin Endocrinol Metab. 1965;25(1):39-45. Read the source ↗
Worked example: FTI 10 — total T4 12 × (T3RU 25% ÷ 30% reference).
Sophie Well is a reference and educational tool. Not medical, legal, or financial advice. Does not replace clinician judgment, professional billing review, or legal counsel.