Thyroid Hormone: How To Calculate Your Reverse T3 Ratio


Issue # 135 September 16, 2013

Welcome to KnowYourThyroid.

Good Monday Morning to everyone.

Today, Louise O’Connor will explain the┬áReverse T3 ratio and the importance of taking the correct thyroid hormone to improve your hypothyroidism symptoms.



How to calculate your reverse T3 ratio

By Louise O’Connor


Triiodothyronine (T3) is the more potent thyroid hormone when compared to thyroxine (T4). T3 helps ‘rev’ up your body. In fact, most of the biological activity of your thyroid hormones is due to T3.

Under normal conditions T4 converts to both T3 and ‘reverse T3’ which is the inactive form of T3. The body maintains a healthy T3 to reverse T3 ratio to control an optimal metabolic rate. This means reverse T3 is quickly eliminated if it is not required to slow metabolism.

What happens when a greater amount of T4 is shunted towards production of reverse T3 and this thyroid hormone pools in the body?


When T4 converts to excessive amounts of reverse T3 this thyroid hormone blocks the effects of T3. Ongoing excess production of reverse T3 leads to a low thyroid disorder called ‘reverse T3 dominance’. Reverse T3 dominance is associated with many of the symptoms commonly associated with an underactive thyroid.

Testing for reverse T3

Only a specific blood test for reverse T3 (rT3) will identify high levels of this inactive form of T3. Most importantly, an assessment of reverse T3 takes on far greater meaning when the total amount of reverse T3 is compared to the total amount of ‘free T3‘.

There is a simple equation to work out your reverse T3/free T3 ratio. You will need your blood test results for both free T3 and reverse T3 to do this.

How to calculate your reverse T3 ratio

To work out the reverse T3 ratio divide the total free T3 by the total reverse T3 and multiply this by 100. The ratio should be between 1.06 to 2.2 and ideally towards the upper end of this range. If this reverse T3 ratio is at the lower end or below this range it strongly indicates reverse T3 dominance is occurring.

Your thyroid blood results can be a little confusing. Here is a real example to help explain how you can calculate your own reverse T3 ratio.

The free T3 test result is 4.3 pmol/L and reverse T3 is 704 pmol/L. To work out the reverse T3 ratio divide 4.3 by 704 then multiply this by 100. The result is 0.6 which is well below the healthy range. This is not good and indicates a definite reverse T3 dominance problem.

Single T3 thyroid medication

Levothyroxine (T4) medication or even alternative T4/T3 thyroid medication is not recommended when you have high levels of reverse T3. Taking supplemental T4 provides the body with a greater amount of T4 with the potential to pool even more reverse T3. This perpetuates the cycle of reverse T3 production.

Switching to T3 only medication ensures you are supplying the body with T3, not more T4. Single T3 thyroid medication may take a little while to work as the reverse T3 clears from the T3 receptors.

Louise O’Connor is a leading Australian Naturopath & Wellness Coach who specialized in thyroid health. The Natural Thyroid Diet is her top-selling e-book that contains a wealth of information on recovering your thyroid health from a holistic, Naturopathic viewpoint. Louise believes that when you are empowered with credible information and an awareness of new opportunities it really is possible for you to finally take control of your thyroid health… to reclaim the vibrant health YOU deserve!

To learn more from Louise be sure to check out her e-book: The Natural Thyroid Diet