Free T4
Free T4 is the thyroid’s main hormone in its free form, not bound to proteins, which the tissues can use.
At a glance
- Sample
- Blood
- Units
- ng/dL (US), pmol/L (Europe)
- Often looked at with
- TSH, Free T3
- Preparation
- No special preparation is usually needed. If other tests are done from the same sample, you may be asked to come fasting.
Units: ng/dL and pmol/L
US labs usually print free T4 in ng/dL, most European labs in pmol/L. To convert, multiply ng/dL by 12.872.
pmol/L = ng/dL × 12.872 · molar mass 776.87 g/mol
This converter changes units only. It doesn’t tell you whether a number is in or out of any range: that depends on the range printed by your own lab, and on your doctor. Soma does not diagnose and is not medical advice.
Why lab ranges differ
Each lab sets its reference range for its own method and analyser, and many ranges differ by age and sex. Two labs can print different ranges for the same blood, so a result is read against the range on its own report, not against a number from another lab or a website.
Soma charts every free T4 result against the range printed by the lab that measured it.
What can affect the result
- Biotin supplements: can give a falsely high result.
- A thyroid hormone tablet shortly before the test.
- Different lab methods.
If something like this applies, mention it to the doctor who reads your results.
Questions
How do I convert free T4 from ng/dL to pmol/L?
Multiply ng/dL by 12.872. For example, 1.2 ng/dL is 15.4 pmol/L.
Why does my lab’s free T4 range differ from another lab’s?
Each lab sets its range for its own method and equipment, and many ranges differ by age and sex. That’s why a result is best read against the range printed on the same report.
How do I prepare for a free T4 test?
No special preparation is usually needed. If other tests are done from the same sample, you may be asked to come fasting. Follow your lab’s instructions.
Related tests
Got a lab report with Free T4?
Share it to Soma: it reads every row on your phone, with no account and no upload, and puts your free T4 on one chart with your earlier results, each against the range your lab printed.
Sources
- Thyroxine (T4) Test — MedlinePlus, U.S. National Library of Medicine.
- Units: PubChem: Thyroxine (thyroxine), molar mass 776.87 g/mol, as the Soma app converts.
Mention of a source doesn’t mean it endorses Soma. This page explains the test; it doesn’t diagnose and is not medical advice. Talk to your doctor about what your results mean.