Free Triiodothyronine (FT3)
- Sample Type
- Standard
- Fasting
- No
- Unit
- pg/mL
FT3 is the metabolically active, unbound fraction of T3. While T4 is more abundant, T3 is much more potent at the cellular level. This test is vital for diagnosing hyperthyroidism (specifically T3-toxicosis) and for monitoring patients on thyroid replacement therapy. It bypasses the confounding effects of binding proteins (like TBG) that affect Total T3 levels.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Non-thyroidal illness syndrome (euthyroid sick syndrome) can cause low FT3 in hospitalized or severely ill patients despite a normal thyroid gland. Additionally, high doses of Biotin (Vitamin B7) supplements can cause analytically false-high FT3 results in many lab assays.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Free Triiodothyronine (FT3):
Official Sources
Research & Guidelines
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Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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