Reverse T3
An inactive form of T3 produced from T4, which rises during stress, illness or calorie restriction.
| Typical reference range | 8–25 ng/dL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
When T4 is converted by the deiodinase enzyme D3, it forms reverse T3, which has no thyroid hormone activity. The body increases this pathway to conserve energy.
Why it matters
Reverse T3 is used to investigate non-thyroidal illness and is popular in functional medicine for assessing T4-to-T3 conversion, although its clinical value outside of hospital settings is debated.
What a high result can mean
High values occur with acute or chronic illness, calorie restriction, intense training, high cortisol or stress, liver or kidney disease, high-dose levothyroxine, and medications such as amiodarone, beta blockers and corticosteroids.
What a low result can mean
Low values occur with hypothyroidism and are generally not a concern.
What affects the result
Interpret alongside free T3 and free T4; the free T3/reverse T3 ratio is sometimes calculated. Energy availability and recovery strongly influence results.
Units and conversion
Usually reported in ng/dL.
- From pmol/L: multiply by 0.065 to get ng/dL
- From ng/mL: multiply by 100 to get ng/dL
Also called on lab reports
T3, Reverse, Reverse Triiodothyronine, rT3, Reverse T3, Serum, T3 Reverse
Related tests: Thyroid
This page is educational and does not replace advice from a healthcare professional.