BiomarkersTotal T4
Thyroid
Total T4
All T4 hormone, bound and free
On your report it may say: Total thyroxine, T4
Total T4 measures both bound and free thyroid hormone. It's affected by pregnancy and the pill, so free T4 is usually preferred.
Typical ranges · µg/dL
nmol/L = µg/dL × 12.87
Oral contraceptives and pregnancy raise total T4 without changing thyroid function.
Ranges vary by lab, age and sex. The range printed on your report applies.
If it's low
May mean an underactive thyroid or low binding proteins.
Common causes
- Underactive thyroid
- Low binding proteins
What you might notice
- Tiredness
- Feeling cold
If it's high
May mean an overactive thyroid or high binding proteins.
Common causes
- Overactive thyroid
- Pregnancy or oral contraceptives
What you might notice
- Fast heartbeat
- Weight loss
Testing
- Who should test
- Usually ordered with TSH in some labs' thyroid panels.
- How to prepare
- Stop biotin 2–3 days before.
- When to retest
- As your doctor advises.
What can help
SYNC doesn't recommend supplements from thyroid results. Thyroid problems need a doctor's diagnosis and treatment.
Discuss abnormal results with your doctor.
Common questions
Why might total T4 be high in pregnancy?
Binding proteins rise, lifting the total.
Is free T4 better?
Usually yes.
Explore further
Sources
Free nutrition assessment
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Build My Nutrition PlanFor general education only, not medical advice. Ranges shown are typical for adults; the range printed on your lab report applies. Talk to a qualified doctor about your results.