sT4
Free thyroxine
- Group
- Thyroid
- Sample
- Blood · with TSH
- unit
- ng/dL
sT4Free thyroxine
ng/dL
About 0.9–1.7 ng/dL (lab-specific)
Source: Laboratory reference ranges
What does it measure?
The free (unbound) part of the main hormone released by the thyroid.
Relationship to nutrition
fT4 is read together with TSH. Diet has limited direct effect, but iodine deficiency or excess (supplements, seaweed products) can affect thyroid function.
Before the test
- Given at the same time as TSH.
This page is general information. Reference ranges vary by laboratory, age, sex and pregnancy; the range on your report is the one that applies. Diagnosis and treatment are carried out by your doctor. No values are entered on this page and no data is sent to the server.