Free T3

Normal range: 1.7-3.7 pg/mL

Source: RUSH, Rush University System for Health, Normal Ranges for Common Laboratory Tests , Pages - RMLRangesBMP (,

This data is published for information purposes only and concerns only adults (> 21 yo). Standards may vary depending on the equipment used.

Understanding Free T3: The Essential Guide to Thyroid Function Tests


When it comes to thyroid health, Free T3 is a term you'll often hear. But what exactly is Free T3, and why is it important? This comprehensive guide aims to answer all your questions about Free T3, its role in thyroid function, and how various medications can interfere with its levels.

What is Free T3?

Triiodothyronine, commonly known as T3, is one of the two primary hormones produced by the thyroid gland. Free T3 refers to the unbound form of T3 circulating in the bloodstream, which is available to enter cells and carry out its metabolic functions.

Why is Free T3 Important?

Free T3 plays a crucial role in regulating metabolism, energy production, and other essential bodily functions. It is often measured alongside other thyroid hormones like T4 and TSH (Thyroid Stimulating Hormone) to provide a complete picture of thyroid health.

How is Free T3 Measured?

A Free T3 test is a blood test that measures the level of Free T3 in your bloodstream. It is usually part of a broader thyroid panel that also includes TSH and Free T4 tests.

Normal Free T3 Levels

Normal Free T3 levels typically range from 1.7-3.7 pg/mL, although this can vary depending on the laboratory and individual factors like age and sex.

Medications That Can Interfere with Free T3 Levels

It's important to note that certain medications can interfere with Free T3 levels, potentially leading to inaccurate test results. These include:

  • Amiodarone
  • Antithyroid medications (e.g., Methimazole, Propylthiouracil)
  • Beta blockers (e.g., Propranolol)
  • Birth control pills
  • Steroids (e.g., Prednisone)
  • Some anticonvulsants (e.g., Phenytoin, Carbamazepine)

Always consult your healthcare provider about any medications you are taking prior to undergoing a Free T3 test.


Understanding Free T3 is essential for anyone looking to get a comprehensive view of their thyroid health. Always consult with a healthcare professional for accurate diagnosis and appropriate treatment.

  1. Thyroid Function Tests - American Thyroid Association
  2. Thyroid Tests - National Institute of Diabetes and Digestive and Kidney Diseases
  3. Medications That Affect Thyroid Function Testing - NCBI

Disclaimer: This blog post is for informational purposes only and should not be considered as medical advice. Always consult with a healthcare professional for medical advice and treatment.

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