What is reverse T3?
Reverse T3 (RT3) is a normal by-product of thyroid hormone production and an important
regulatory mechanism in the body.
It is produced to stop our bodies from becoming hyperthyroid. Even patients with a
well-functioning thyroid will still be producing reverse T3.
The problem comes when reverse T3 production is increased relative to T3 levels. This
means that the T4 is being used up to make RT3 and not the active T3 hormone.
This is problematic because of two reasons
- T3 is not being produced
- It is thought that RT3 blocks the T3 receptor sites on cells meaning that T3
cannot work on the cells.
Both will cause worsening hypothyroid symptoms.
What Causes Elevated Reverse T3?
It is not normal for excessive thyroid hormone to be shunted towards reverse T3
production, but this can happen for a number of reasons including:
Over treatment with levothyroxine/NDT – the more thyroid hormone the more
reverse T3 will be produced as well. This is not always a problem if T3 levels are
within a good range.
- Stress -our stress hormone cortisol increases conversion of T4 into reverse T3
- Poor blood sugar management and insulin resistance ( eg in PCOS)
- Starvation or crash dieting – fasting and low carb diets increase DI03 activity to
- Chronic illness
- Certain medications (such as glucocorticoids, Amiodarone and certain beta-
All of these factors contribute to increased conversion of T4 to reverse T3, potentially
resulting in symptoms of hypothyroidism or thyroid dysfunction.
How Do You Test For Reverse T3?
Reverse T3 can be tested but it is an expensive test (around £150) and often in the
context of symptoms and other thyroid hormone tests a practiced clinician can tell that
your RT3 will be high. However it can be an interesting and informative test to have
done, so if you are interested in doing so please ask your clinician for further