thyroid
Free Triiodothyronine
Free Triiodothyronine is a thyroid biomarker expressed in pg/mL.
- Short name
- FT3
- Unit
- pg/mL
- Reference min
- 2.3
- Reference max
- 4.2
- Optimal min
- 3.0
- Optimal max
- 4.0
- Better when
- higher is better
- Reference min (male)
- 2.3
- Reference max (male)
- 4.2
- Reference min (female)
- 2.3
- Reference max (female)
- 4.2
- Sample
- serum
- Fasting required
- false
- Related markers
- Thyroid Stimulating Hormone, Free Thyroxine, Reverse T3
Moved by
Interventions that trials measured against this marker, and which way it moved.No trial has measured Free Triiodothyronine against an intervention in this library yet.
Full write-up
What is it
Free Triiodothyronine, often abbreviated FT3, is a thyroid biomarker. It represents a measured value for free triiodothyronine and is used to describe this thyroid-related marker in the body.
How to test it
Free Triiodothyronine is measured from a serum sample, collected through a blood test. Fasting is not required, so the test can be arranged without fasting preparation.
When reviewing the result, use the reference and optimal ranges shown alongside it rather than interpreting the number in isolation. Free Triiodothyronine may also be considered together with Tsh, Free T4, and Reverse T3, which can provide related context for understanding the result. If the test is being arranged because of a medical condition or concern, discuss the appropriate testing approach and interpretation with a clinician.
Reading your result
Free Triiodothyronine results are most useful when read against the reference range and unit printed on the same laboratory report. A reference range describes a broader interval for interpretation, while an optimal range is narrower. These ranges are not interchangeable, so a result can fall within the reference range without also falling within the optimal range.
Laboratories may use different ranges or units, which is why a number should not be interpreted in isolation or compared directly with a result reported elsewhere. The reference framework treats higher values as more favorable, but that direction alone does not establish what an individual result means.
A single value is not a diagnosis. Results outside the reference range belong with a clinician, who can interpret them in context.
What moves it
Selenium was measured directly in relation to Free Triiodothyronine, and the marker was unchanged. Because higher Free Triiodothyronine is considered better, this evidence does not demonstrate an improvement in the marker with Selenium.
This finding reflects direct measurement of Free Triiodothyronine, rather than an indirect effect on a related outcome. It should therefore be distinguished from evidence about thyroid-related effects that were not measured through this specific marker. The result describes the observed group-level finding and does not determine how an individual’s Free Triiodothyronine may respond.