What is Reverse T3?

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If you have been diagnosed with a thyroid problem, then you have probably heard about the terms “reverse T3” and maybe even “reverse T4.”

If these sounds gibberish (if not worrisome) for you, fret not as this article will help you learn more about reverse T3 and reverse T4 – in terms you can comprehend.

Thyroid Hormones and Associated Disorders

The basics matter, so before we push forth, you need to have a clear overview of the Thyroid gland first.

Note that it is located at the neck base, in front of the trachea and below the Adam’s Apple.

It produces two hormones (mentioned below) in response to the Thyroid Stimulating Hormone produced by the brain’s pituitary gland.

T3 (Triiodothyronine)

This hormone affects many body processes, including heart rate, body temperature, metabolism, growth, and development.

Also known as the ‘true thyroid hormone,’ it is four times more potent than T4. The normal levels of T3 in the body range from 80-180 ng/dl.

T4 (Thyroxine)

The primary hormone produced by the gland, it is synthesized in the thyroid follicular cells.

It works by stimulating oxygen consumption, thereby resulting in cell and tissue metabolism. In the blood stream, it is converted to T3 with the help of target cells or liver enzymes.

The level of T4 in the body differ according to experts, but the normal acceptable values are from 4.6 to 11.2 mcg/dl.

Low levels of these hormones signify Hypothyroidism, which is usually brought about by an inactive or underactive thyroid.

This can take place due to thyroid gland inflammation or removal, hyperthyroidism treatment, or cancer treatment. Symptoms of hypothyroidism include slowed heart rate, weight gain, fatigue, cold intolerance, menstrual disturbances, to name a few.

High levels of these hormones, on the other hand, establish Hyperthyroidism.

Also known as thyrotoxicosis, it is common in women or peopled aged 60 years old and above.

Simple goitera, thyroid gland inflammation, Graves Disease or Plummers Disease can lead to the development of this condition.

Symptoms range from heat intolerance, nervousness, diarrhea, hand tremors, and mood swings, to name a few.

There are many treatment options for boosting thyroid hormones, including natural methods.

Reverse T3


Reverse T3, also known as rT3, is formed through the process of deiodination, or the removal of iodine, from the 5 position of T4 or thyroxine.

It is different from T3 or Triiodothyronine in terms of the attachment of the atoms to the aromatic rings.

Reverse T3 is converted from the hormone T4 by the liver in order to eliminated the unneeded amounts of the latter.

About 20% of T4 in the body is converted to rT3, which is metabolically inactive.

But since it is the reverse of T3, it can attach to T3 receptor sites. However, it will not bring any change as it does not produce any biological activity.

Although this is the case, it plays a protective role, as concluded in the study of Desai et al.

In this study, it was shown that T4 replacement produces higher amounts of rT3, which prevents the rise in T3. As a result, majority of patients with congenital hypothyroidism who, despite being ‘overtreated’ with Levothyroxine, did not manifest signs of hyperthyroidism.

Because of this finding, among many others which you will find in the other chapters, rT3 is significant for clinicians as it helps determine hypothyroidism from acute illnesses that bring about pronounced thyroid changes.

Importance of Determining rT3 Levels

A rT3 exam is needed to ascertain the levels of the said hormone in the body. So why is this necessary, even if you have undergone the routine serum T3 and T4 testing?

A study by Schlienger et al showed some hyperthyroidism cases have normal/low levels of T3, and elevated levels of T4 and rT3.

In other words, diagnosis of hyperthyroidism might not be established as clinicians usually attribute this to high levels of T3. The researchers went on to solidify the importance of the rT3 exam due to the “lack of diagnostic discrimination of T3 assays in thyroid dysfunction especially in the older patient or one with associated disease.”

Additionally, rT3 levels imitate T4 levels.

Consequently, a low T3 to rT3 ratio is seen in patients with hypothyroidism, and in effect a high ratio is observed individuals with hyperthyroidism.

Such findings have been discussed in the study of Shimada entitled “The Conversion of Thyroxine to Triiodothyronine or to Reverse T3 Patients with Thyroid Dysfunction.”

In this study, he concluded that “the relationship between serum T4 level and rT3/T3 ratio should be examined for adequate information concerning the peripheral conversion of thyroid hormones under various thyroid diseases.”

Because rT3 determination strengthens diagnosis, your physician might ask you to undergo a Reverse T3 exam in order to provide a clearer picture of your condition. This will help him provide you with the best management available.

In the rT3 test, you can expect 0.4 to 0.8 ml of blood to be drawn from your arm.

It will be placed by your healthcare provider in a plastic vial with a red top. It will take 2 days for the analysis to be completed.

The medical technologist will then measure your serum rT3 levels against the optimal values of 14 to 25 ng/dl.

But before you undergo this exam, make sure to inform your healthcare provider about the medications and herbs you are currently taking.

As with other blood exams, the rT3 test comes with the risks of infection, bruising, bleeding, and site swelling.

Why do Reverse T3 Levels Increase?

So why is there a spike in rT3 in some people? Such occurs in the following cases:

Anorexia nervosa and Starvation

Whether it’s wanted or unwanted, decreasing your caloric intake at an extreme can take a toll on thyroid health.

To conserve energy, the body will increase the production of rT3 and decrease the production of T3.

An increase in rT3 in these cases can also be attributed to the low levels of zinc, selenium, and iron in the body.

These minerals play a major role in powering an enzyme to convert T4 to T3. Where there are lower levels of T3, and higher levels of rT3 flood the bloodstream instead.

Increased stress: Burns, Hemorrhagic shock, Postoperative stress, Severe infection or Severe trauma

In critically sick patients, increased rT3 levels coupled with low T3 levels establishes the finding of “Sick Euthyroid Syndrome” or “Non-Thyroidal Illness.”

This occurs because the body produces more rT3 (50% from the normal 20%) than T3 in order to prevent the tissues depending on the latter to become metabolically active.

To cope up with the stress, the body will release cortisol, otherwise known as the “fight or flight hormone.”

While it is very helpful, it can interfere with normal thyroid activity if it remains in the system for a prolonged period of time.

Because of cortisol flooding, more T4 is converted to rT3. This is the body’s way of conserving energy until the stresses caused by aforementioned conditions are finally resolved.

Chronic Diseases: Diabetes, Hepatic dysfunction, Lyme Disease or Renal Failure

These chronic illnesses result in an increase in reverse T3, again because the body tries to adapt to the ‘stresses’ brought about by the said maladies.

Exposure to Toxins or Heavy Metals

The said substances are harmful to over-all health, especially the thyroid.

Toxins can block cellular receptors, or they can destroy healthy thyroid tissue. These events can sabotage normal thyroid functioning and as a result, rT3 levels in the body can increase exponentially.

Additionally, rT3 levels can rise in people taking the following medications:

  • Amiodarone
  • Dexamethasone
  • Halothane
  • Ipodate
  • Propanolol
  • Propylthiouracil

How to Lower Reverse T3 Levels in the Body

Although rT3 in moderate amounts is protective as mentioned in the study of Desai et al, increased levels can wreak havoc to your health.

If you have been diagnosed with increased rT3 levels and you are not suffering from any of the conditions or taking any of medications listed above, then you need to make a move to normalize the rT3 concentration in your body.

Here are some effective methods to help you attain optimal thyroid health:

T3 Supplementation

T3 Supplementation is done in order to increase T3 levels in the body.

This will decrease the concentration of T4 hormones, as excess of which are converted into Reverse T3.

Should you undergo this therapy, you will need to endure rT3 testing every one to two months. Some of the popular T3 drugs include Cytomel.

Treatment of Underlying Problem

First and foremost, you need to make sure that you are not suffering from any of the above-mentioned conditions that lead to increased levels of rT3.

Symptoms will not be reversed if the underlying problems are not addressed.

In individuals with chronic diseases, efficient management of the ailment is essential.

For example, diabetic patients should follow their medication regimen in order to control their sugar levels.

As for starved or anorexic patients, consumption of the recommended number of calories through mouth or intravenous infusion are recommended.

In individuals with mineral deficiencies, Zinc and Selenium supplementation are recommended as they foster the conversion of T4 to T3 instead of rT3.

For those exposed with toxins and heavy metals, avoiding said sources and certain foods can help normalize rT3 levels in the body.

Lifestyle Changes

Medications, like Armour Thyroid or Synthroid,  and treatments will not work if you do not change yourself for the better.

Thyroid hormones interact with many processes of the body, as such, you need to observe the following in order to lower your rT3 levels:

  • Get adequate sleep every night
  • Eat a healthy diet
  • Exercise
  • Reduce stress and its sources

While lowering rT3 levels is the goal, avoid going below the normal values.


Your body will then exhibit hyperthyroidism symptoms, which include heart palpitations, heat intolerance, irritability, and insomnia, to name a few.

When addressing your high rT3 levels, remember that the goal should be to normalize the balance between your thyroid hormones!

Reverse T4: Is there Such a Thing?

The term Reverse T4 is unheard of by many, but a handful of scientific minds have alluded it to Levothyroxine.

According to the author Janie Bowthorpe, she had a conversation with Biochemistry majors who explained that if reverse T3 is the mirror image of T3, then it follows that Levothyroxine, the mirror image of Thyroxine or T4, should be called Reverse T4.

Although this is a sound argument, many scholars emphasize that there is no such thing as Reverse T4.

But with the many developments in the field of Science and Technology, there is always a possibility that such a hormone can be discovered.


To conclude, Reverse T3 levels is something you should be vigilant about – especially if you have a history of thyroid illness.

While it is protective in adequate amounts, it can be harmful if left in excess.

As such, it is important that you push through with T3 medications your doctor recommendations, nutrition supplementation for the thyroid, lifestyle changes, and the treatment of underlying problems if you want to maintain the healthy levels of rT3 in your body.


Desai, M., Irani, A. J., Patil, K., & Pandya, C. S. (1984). The importance of reverse triiodothyronine in hypothyroid children on replacement treatment. Archives of Disease in Childhood ,59(1), 30-35. Retrieved August 12, 2017, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1628409/.

Schlienger, J. L., Chabrier, G., Stephan, F., & Sapin, R. (1980). Https://www.ncbi.nlm.nih.gov/pubmed/7355063. Nouv Presse Med.,5(9), 30. Retrieved August 12, 2017, from https://www.ncbi.nlm.nih.gov/pubmed/7355063.

Shimada, T. (1984). The conversion of thyroxine to triiodothyronine (T3) or to reverse T3 in patients with thyroid dysfunction. Nihon Naibunpi Gakkai Zasshi,60(3), 195-206. Retrieved August 12, 2017, from https://www.ncbi.nlm.nih.gov/pubmed/6479377.

Test ID: RT3 T3 (Triiodothyronine), Reverse, Serum. (2017). Retrieved August 11, 2017, from http://www.mayomedicallaboratories.com/test-catalog/Clinical and Interpretive/9405

The thyroid gland. (2013, July 15). Retrieved August 12, 2017, from http://www.kumc.edu/school-of-medicine/internal-medicine/endocrinology/patient-education/the-thyroid-gland.html

Thyroid Function Tests. (n.d.). Retrieved August 11, 2017, from https://www.auburn.edu/~deruija/endo_thyroidfts.pdf

Thyroid Hormones. (2017, July 31). Retrieved August 12, 2017, from https://en.wikipedia.org/wiki/Thyroid_hormones

Thyroxine (T4): An Overview. (n.d.). Retrieved August 12, 2017, from http://media.usm.maine.edu/~champlin/Courses%20S’14/Papers/Thyroxine.pdf

  1. Reply
    George Seese September 1, 2020 at 1:04 am

    If the liver changes excess T4 to RT3, why should there be a high level of serum T4? If most of the body’s RT3 is made within the cells, how can serum RT3 be measured? Why does the Thyroid Gland make T3 if T4 provides the flexibility in cells to make either T3 or RT3? Do certain cells prefer T3?

  2. Reply
    carol reuben March 18, 2018 at 10:43 am

    The information that I have just read is excellent and for the Americans who have a RT3 issue you are all really lucky as there seems to be many clinics in the states who not only recognise that high levels of RT3 cause thyroid patients to be very in well but they are willing to treat this condition. I have had my RT3 levels checked twice in recent yeas and on both occasions they have been way over the upper limit of the reference range!! Yes you can get the blood test done in England, that is if you pay private, it is not undertaken by the NHS but unfortunately once you have the results and if like me your levels are high, you have got absolutely no chance of being treated by a doctor!! They are ruled by the General Medical Board/Council who dictate that reverse t3 dominance does not exist
    and therefore there is no treatment protocol. The few doctors who have had the guts to try to address this issue have been dragged through the courts and struck off!! Doctors in this country are not allowed to think outside the box.

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