Reviewed: 16. April 2026
fT4 Free Thyroxine (FT4)
Unit: ng/dl
Quick Explanation
fT4 (free thyroxine) is the main thyroid hormone and is converted in the liver to the active fT3. Elevated levels may indicate hyperthyroidism, low levels may point to hypothyroidism. This value should always be assessed alongside TSH.
📊 Reference Values
ℹ️ Reference ranges may vary slightly between laboratories. Always compare your value with the reference range from your own lab report.
🔍 Possible Causes
Value too high — possible causes
- ·Hyperthyroidism
- ·Graves' disease
- ·Excess thyroid hormone dosage
Value too low — possible causes
- ·Hypothyroidism
- ·Hashimoto's thyroiditis
- ·Pituitary gland disease
This list shows possible causes — not a diagnosis. Only your doctor can correctly interpret your result.
🩺 Questions for Your Doctor
- →How does my fT4 relate to my TSH level?
- →Do I need thyroid hormones?
- →Should I have a thyroid ultrasound?
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Medical Disclaimer
The content on this page is for general information only and does not replace professional medical advice, diagnosis, or treatment. Always consult your doctor or pharmacist for health-related questions. Lab values should always be assessed in the context of your personal medical history.