Free T4
Free T4 (thyroxine) is the unbound, active form of the main thyroid hormone that regulates metabolism.
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Conventional Range
0.8 - 1.8 ng/dL
Optimal Range
1.0 - 1.5 ng/dL
Why It Matters
Free T4 directly reflects thyroid hormone availability and is essential for metabolism, growth, and development.
If Your Level Is High
High Free T4 with low TSH indicates hyperthyroidism, causing increased metabolism and associated symptoms.
Possible Causes
- Hyperthyroidism
- Graves' disease
- Thyroiditis
- Excessive medication
If Your Level Is Low
Low Free T4 with high TSH indicates hypothyroidism, causing slowed metabolism.
Possible Causes
- Hypothyroidism
- Hashimoto's
- Iodine deficiency
- Pituitary dysfunction
How to Optimize
Treatment depends on underlying cause. Hypothyroidism requires thyroid hormone replacement; hyperthyroidism may need medication, radioiodine, or surgery.
Dietary Factors
- Iodine
- Selenium
- Zinc
- Vitamin D
Lifestyle Factors
- Stress management
- Environmental factors