Total Triiodothyronine (T3)
- Sample Type
- Standard
- Fasting
- No
- Unit
- ng/dL
T3 is the metabolically active form of thyroid hormone. While T4 is more abundant, T3 is significantly more potent. In a Thyroid Function Test, Total T3 measures both bound and unbound forms. It is particularly useful for diagnosing T3 toxicosis, a form of hyperthyroidism where T4 is normal but T3 is elevated, and for monitoring the severity of hyperthyroid states.
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Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Total T3 is highly sensitive to changes in binding proteins (TBG). Pregnancy, oral contraceptives, and HRT can falsely elevate Total T3, while 'Euthyroid Sick Syndrome' during severe systemic illness can cause levels to plummet even if the thyroid is healthy. Biotin supplements can also cause interference.
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 Total Triiodothyronine (T3):
Official Sources
- T3 Test - Testing.comTesting.com
- T3 test: MedlinePlus Medical EncyclopediaMedlinePlus
Research & Guidelines
Related Indicators
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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