Total T4
The total amount of thyroxine in the blood, both bound and free.
| Typical reference range | 4.5–12 ug/dL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Total T4 measures thyroxine bound to carrier proteins (thyroxine-binding globulin, albumin, transthyretin) plus the small free fraction.
Why it matters
Total T4 reflects thyroid output but is strongly affected by changes in binding proteins, so free T4 is generally preferred.
What a high result can mean
High values occur with hyperthyroidism, or with increased binding proteins from pregnancy, estrogen, oral contraceptives or hepatitis (with normal free T4).
What a low result can mean
Low values occur with hypothyroidism, or with low binding proteins from androgens, nephrotic syndrome, liver disease or corticosteroids.
What affects the result
Interpret with T3 uptake or free T4. Estrogen and pregnancy raise binding proteins.
Units and conversion
Usually reported in ug/dL.
- From nmol/L: multiply by 0.078 to get ug/dL
Also called on lab reports
T4, Total, Thyroxine, T4, Thyroxine (T4), Thyroxine, Total, T4 Total
Related tests: Thyroid
This page is educational and does not replace advice from a healthcare professional.