Total T4 measures all thyroxine in the blood, both the part bound to proteins and the free part.
- Normal range (adults)
- 5–12 µg/dL (64–154 nmol/L)
- Sample
- Blood
- Fasting
- Not usually needed
- Also called
- T4, Thyroxine, Total Thyroxine, TT4, Serum T4
Total T4 normal range
| Group | µg/dLConventional units: US, South Asia | nmol/LSI units: UK, Europe, Australia, international |
|---|---|---|
| Adults | 5–12 | 64–154 |
Your report may use either unit system; labs in the Gulf often print both. Ranges also vary slightly between laboratories, so the range printed on your own report is the one to go by.
Why is the Total T4 test done?
It is an older test, largely replaced by Free T4, but some labs still report it.
What does a high Total T4 level mean?
High Total T4 may mean an overactive thyroid, or simply more binding protein in the blood.
Common causes
- Hyperthyroidism
- Pregnancy or estrogen pills (raise binding proteins)
- Excess thyroid medicine
Diet and lifestyle tips
- Avoid iodine supplements and seaweed
- Limit caffeine
What does a low Total T4 level mean?
Low Total T4 may mean an underactive thyroid, or low binding proteins.
Common causes
- Hypothyroidism
- Low protein levels from liver or kidney disease
- Some medicines, such as steroids
Diet and lifestyle tips
- Iodised salt, dairy, eggs, seafood
- Adequate protein
When should you see a doctor?
Ask your doctor whether a Free T4 and TSH would give a clearer answer.
Last updated
This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.