Thyroid panel
Free T4
Also called Free thyroxine · measured in ng/dL
What it measures
The unbound fraction of thyroxine available to tissues.
Why it is tracked
Used alongside TSH to characterise thyroid function and distinguish primary thyroid disease from pituitary causes.
What a provider considers
- Ordered when TSH is abnormal
- Affected by pregnancy and some medications
Reference ranges vary between laboratories and a single result rarely means much on its own. Interpretation depends on your symptoms, your other markers and the trend over time — which is what your provider reviews.