Free Thyroxine Index (FTI)
The Free Thyroxine Index (FTI) is a calculated value derived from total T4 and T3 uptake, used to estimate the amount of free (unbound) thyroxine in the blood.
Category: Thyroid Panel
Also known as: free thyroxine index
Reference range: 1.2–4.9 index (Source: ABIM)
Standard unit: index
High values may indicate
High FTI may suggest hyperthyroidism.
Low values may indicate
Low FTI may suggest hypothyroidism.
Frequently asked questions
- What is a normal Free Thyroxine Index (FTI) level?
- A typical reference range for Free Thyroxine Index (FTI) is 1.2–4.9 index (source: ABIM). Reference ranges vary by laboratory, age, and sex, so always compare against the range on your own lab report.
- What units is Free Thyroxine Index (FTI) measured in?
- Free Thyroxine Index (FTI) is most commonly reported in index. Labs in different countries may use other units — you can convert between them with BloodId's blood test unit converter.
- Where do Free Thyroxine Index (FTI) reference ranges come from?
- BloodId uses ABIM standard reference ranges and educational information from MedlinePlus (see our methodology). Reference ranges still vary by lab, age, and sex, so always compare against your own report.
- Can I track Free Thyroxine Index (FTI) over time?
- Yes. Upload results from any lab and BloodId charts your Free Thyroxine Index (FTI) over time against its reference range, so you can see whether the trend is rising, falling, or stable.
Related biomarkers
Source: BloodId admin-reviewed
Analyze your Free Thyroxine Index (FTI) with AI
Chart your Free Thyroxine Index (FTI) over time
Track your Free Thyroxine Index (FTI) over time with BloodId