Free T3
Track Free T3 levels for active thyroid hormone and metabolic rate assessment. Learn how this critical marker reveals your thyroid health.
What is Free T3?
Free T3 (triiodothyronine) is the active, unbound form of the thyroid hormone T3. It represents the small fraction of T3 that’s immediately available to enter cells and regulate metabolism. Free T3 is considered the most metabolically active thyroid hormone and provides the best assessment of thyroid hormone activity at the cellular level.
Why is it Tested?
Doctors order Free T3 to evaluate thyroid function, particularly when symptoms suggest hyperthyroidism or when other thyroid tests are inconclusive. It’s especially useful for diagnosing T3 thyrotoxicosis and monitoring thyroid hormone replacement therapy effectiveness.
Normal Ranges
Reference ranges vary by lab but generally fall within:
- Adults: 2.0–4.4 pg/mL
Free T3 levels remain relatively stable throughout life but may decline slightly with normal aging.
Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.
What do Abnormal Results Mean?
Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.
Low Free T3
Low levels may indicate:
- Hypothyroidism
- Non-thyroidal illness syndrome
- Poor T4 to T3 conversion
- Certain medications (beta-blockers, steroids)
High Free T3
Elevated Free T3 may suggest:
- Hyperthyroidism (Graves’ disease, toxic nodules)
- T3 thyrotoxicosis
- Excessive thyroid medication
- Thyroiditis (temporary elevation)
How to Track Over Time
Free T3 provides insight into metabolic activity and thyroid hormone utilization. Tracking Free T3 alongside other thyroid markers helps optimize thyroid replacement therapy, detect conversion issues, and monitor treatment response more precisely than TSH alone.
Track your Free T3 results over time
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