Total Thyroxine (T4)
- Sample Type
- Standard
- Fasting
- No
- Unit
- µg/dL
Total T4 measures the entire amount of thyroxine circulating in the blood, including the portion bound to transport proteins (like TBG) and the 'free' physiologically active portion. It is a cornerstone of the Thyroid Function Test panel to assess hyperthyroidism or hypothyroidism. It reflects the thyroid gland's secretory capacity under the regulation of TSH.
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Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Total T4 is highly sensitive to changes in binding proteins. Pregnancy, oral contraceptives, or hormone replacement therapy increase Thyroid Binding Globulin (TBG), which will falsely elevate 'Total T4' while 'Free T4' remains normal. Conversely, anabolic steroids or severe illness can lower TBG, falsely depressing Total T4.
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 Thyroxine (T4):
Official Sources
- T4 Test - Testing.comTesting.com
Research & Guidelines
- PubMed: Total Thyroxine (T4) Clinical GuidelinesNCBI / PubMed
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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