Metabolic Health

Free Thyroxine Index

Optimal Result: 1.2 - 4.9 Units.

Free thyroxine index is considered to be a reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding. The free thyroxine index has generally been replaced by Free Thyroxine in the assessment of thyroid function, but is occasionally useful when a free T4 result is suspected of being anomalous.

Reference ranges for the free thyroxine index:

  • 0-5 days: 5.1-20.8 mcg/dL
  • 6 days-2 months: 5.5-18.0 mcg/dL
  • 3-11 months: 5.7-16.8 mcg/dL
  • 1-5 years: 5.9-15.0 mcg/dL
  • 6-10 years: 6.0-13.9 mcg/dL
  • 11-19 years: 5.9-13.2 mcg/dL
  • > or =20 years: 4.8-12.7 mcg/dL

How to calculate the free thyroxine index?

The free thyroxine index (FTI) is determined by the following calculation:

 

 

What does it mean if your Free Thyroxine Index result is too low?

Low levels are caused by hypothyroidism. Low results may also occur in hospitalised patients with non-thyroidal illness.

What does it mean if your Free Thyroxine Index result is too high?

High levels are caused by hyperthyroidism.

Understand blood, stool, and urine medical results from your labs.

10 000+ happy clients
100% satisfaction
★★★★★ customer support

Essential Plan


  • Monthly subscription
  • Instant interpretation
  • Use the free self-upload form
  • Additional charge for upload service
  • 2000+ biomarkers explained
  • Recommendations
  • Cancel anytime

Advanced Plan


  • Yearly subscription
  • Instant interpretation
  • We upload five reports for you
  • Use the free self-upload form
  • 2000+ biomarkers explained
  • Nutrition Recommendations
  • Online support
  • Cancel anytime

Own It For Life premium plan


  • No subscription
  • Unlimited access
  • Unlimited storage
  • Instant interpretations
  • We upload ten reports for you
  • Use the free self-upload form
  • 2000+ biomarkers explained
  • Nutrition Recommendations
  • Dedicated support

Healthmatters.io software for professional use.

Welcome to Healthmatters Pro.

Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place.

Learn More


We implement proven measures to keep your data safe.

At HealthMatters, we're committed to maintaining the security and confidentiality of your personal information. We've put industry-leading security standards in place to help protect against the loss, misuse, or alteration of the information under our control. We use procedural, physical, and electronic security methods designed to prevent unauthorized people from getting access to this information. Our internal code of conduct adds additional privacy protection. All data is backed up multiple times a day and encrypted using SSL certificates. See our Privacy Policy for more details.

General Data Protection Regulation (GDPR). HIPAA compliance for healthcare professionals
×

Understand Your Lab Result Now

  • Instant interpretation
  • 2000+ biomarkers explained
  • Science-based recommendations
  • Online support
  • Secure and private portal

Get 10% off with promocode:

;