What Is a Normal Free T4 Level?
The normal Free T4 range is 0.8–1.8 ng/dL. Values below or above this range may indicate a condition that requires further evaluation.
Reference Range Table
| Marker | Low | Normal | High |
|---|---|---|---|
| Free T4 | Below 0.8 ng/dL — hypothyroidism | 0.8–1.8 ng/dL | Above 1.8 ng/dL — hyperthyroidism |
What Affects Your Results
Thyroid medication timing (test before daily dose), pregnancy, biotin supplements (can interfere with assay), estrogen therapy, severe illness, and certain medications.
When to Retest
When adjusting thyroid medication, 6-8 weeks. Once stable, every 6-12 months alongside TSH.
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