Mediki
T4 blood test: what your result means
T4 measures thyroxine, the main thyroid hormone precursor in circulation.
- Category
- Thyroid
- Standard unit
- nmol/L
- Reported in
- nmol/L, µg/dL, µg/100mL, µg%, ng/mL, µg/L
What does high T4 mean?
Higher values may suggest increased thyroid hormone production or release. What counts as high depends on the reference range printed on your lab report, because ranges differ between laboratories.
What does low T4 mean?
Lower values may suggest reduced thyroid hormone production. What counts as low depends on the reference range printed on your lab report, because ranges differ between laboratories.
T4 units and conversion
Mediki shows T4 in nmol/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 nmol/L | Convert back |
|---|---|---|
| µg/dL, µg/100mL, µg% | 1 µg/dL = 12.87 nmol/L | 1 nmol/L = 0.0777 µg/dL |
| ng/mL, µg/L | 1 ng/mL = 1.287 nmol/L | 1 nmol/L = 0.7769 ng/mL |
Convert a value from your report with the blood test unit converter.
Why track T4 over time?
A single 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 T4 as part of a panel? See the thyroid test tracker.
Track your T4 results in one chart
Upload your lab reports and Mediki plots every T4 result against its reference range. Your first 15 pages are free.
Try 15 pages freeRelated blood tests
Sources
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.