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Free Triiodothyronine (FT3)

Published: July 27, 2026Updated: August 25, 2026

This biomarker measures the concentration of unbound triiodothyronine hormone in the blood, which plays a crucial role in regulating metabolism and energy production.

Quick summary

FT3 is a key indicator of thyroid function and metabolism.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
pg/mL
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
Roche FT3, Abbott FT3, Siemens FT3, Beckman FT3
interpretation: {"text":"May indicate hypothyroidism, iodine deficiency, or certain medications affecting thyroid function.","label":"Low FT3"}; {"text":"May suggest hyperthyroidism, thyroid nodules, or Graves' disease.","label":"High FT3"}

Free Triiodothyronine (FT3) is a hormone produced by the thyroid gland and is one of the primary forms of thyroid hormone circulating in the blood. It is not bound to proteins, making it readily available for use by the body's cells.

FT3 is essential for regulating metabolism, growth, and development. It influences almost every physiological process in the body, including heart rate, digestion, and temperature regulation.

Abnormal levels of FT3 can indicate thyroid disorders such as hyperthyroidism or hypothyroidism. Measuring FT3 levels is crucial for diagnosing and managing these conditions.

Frequently asked questions

What is the normal range for FT3?
The normal reference range for FT3 is typically 2.3–4.2 pg/mL.
How is FT3 testing performed?
FT3 testing is done through a blood sample, usually taken from a vein in the arm.
  1. 1
    American Thyroid AssociationSource
  2. 2
    Mayo ClinicSource

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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

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Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy