Mediki
Free T4 blood test: what your result means
Free T4 measures the unbound fraction of T4 that can enter tissues and convert to T3.
- Category
- Thyroid
- Standard unit
- pmol/L
- Reported in
- pmol/L, ng/dL, ng/100mL, ng%, ng/mL, ng/L and more
What does high free T4 mean?
Higher values may suggest increased available thyroid hormone. What counts as high depends on the reference range printed on your lab report, because ranges differ between laboratories.
What does low free T4 mean?
Lower values may suggest reduced available thyroid hormone. What counts as low depends on the reference range printed on your lab report, because ranges differ between laboratories.
Free T4 units and conversion
Mediki shows free T4 in pmol/L. Labs may report it in other units; Mediki converts them automatically so results from different labs line up on one chart.
| Unit on your report | Convert to pmol/L | Convert back |
|---|---|---|
| ng/dL, ng/100mL, ng% | 1 ng/dL = 12.87 pmol/L | 1 pmol/L = 0.0777 ng/dL |
| ng/mL | 1 ng/mL = 1,287 pmol/L | 1 pmol/L = 0.000777 ng/mL |
| ng/L, pg/mL | 1 ng/L = 1.287 pmol/L | 1 pmol/L = 0.777 ng/L |
Convert a value from your report with the blood test unit converter.
Why track free T4 over time?
A single free T4 result is a snapshot. Comparing it with your earlier tests shows whether a value is stable, slowly drifting, or responding to a change in treatment or lifestyle, which is often more useful than one number on its own.
Read our guide on how to read blood test results to understand reference ranges, flags and units.
Following free T4 as part of a panel? See the thyroid test tracker.
Track your free T4 results in one chart
Upload your lab reports and Mediki plots every free T4 result against its reference range. Your first 15 pages are free.
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Medical disclaimer: This page is general information, not medical advice. Reference ranges differ between laboratories, and only a doctor can interpret your results in the context of your health.