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Reverse T3 or perverse T3? Still puzzling after 40 years

Four decades after reverse T3 (3,3′5′-triiodothyronine) was discovered, its physiologic and clinical relevance remains unclear and is still being studied. But scientific uncertainty has not stopped writers in the consumer press and on the Internet from making unsubstantiated claims about this hormone. Many patients believe their hypothyroid symptoms are due to high levels of reverse T3 and want to be tested for it, and some even bring in test results from independent laboratories.

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 Do you have a Reverse T3 problem?

Keep in mind that Reverse T3 itself is not evil. It is part of a healthy thyroid hormone metabolism. Every healthy person makes some every day, and that’s why there is a normal reference range for Reverse T3. However, “excess” Reverse T3, and the bigger picture of thyroid hormone inactivation, IS something that thyroid patients should be concerned about.

 What is the Reverse T3 Syndrome?

It is known that the ratio of T3 to RT3 should be >10. There should be at least 10-times as much T3 as RT3 in our bloodstreams. When I have measured these hormone in the patients described above I most often find their T3/RT3 ratios to be <10. I refer to this as the RT3 Syndrome. Raising their T3/RT3 ratios to >10 makes their low thyroid symptoms and signs go away.

Articles of Interest

Overview of Reverse T3 Thyroid Hormone

The body also converts T4 into rT3, which is 3,3',5'-triiodothyronine, an inactive form of T3 that is incapable of the metabolic activity normally carried out by T3. Researchers believe the body produces rT3 in times of severe illness or starvation as a mechanism for preserving energy.

Reverse T3 does not reliably differentiate hypothyroid sick syndrome from euthyroid sick syndrome

Although reverse T3 may be elevated in the setting of nonthyroidal illness, it is not reliable in distinguishing between the hypothyroid sick patient and the euthyroid sick patient. This is probably because of drug and disease effects on thyroid hormone metabolism as well as the presence of sufficient T4 substrate for conversion to reverse T3 in many hypothyroid sick patients.

Reverse T3 Dominance

Reverse T3 dominance, also known as Wilson’s Syndrome, is a condition that exhibits most hypothyroid symptoms although circulating levels of T3 and T4 are within normal test limits. The metabolism of T4 into rT3 is in excess when compared to T3 therefore it is a T4 metabolism malfunction rather than a straight forward thyroid deficiency.

Reverse T3 in Patients With Hypothyroidism, Helpful or a Waste of Time?

Measuring rT3 may be helpful in patients who are already on thyroid treatments, and is of greater importance in patients taking synthetic preparations. It is not recommended in patients who are not taking thyroid medicine (even if experiencing hypercortisolism) or in patients with hypopituitarism that are taking adequate hormone replacement.

What does a high reverse T3 mean?

The problem with rT3 is that it will bind to T3 receptors but it has no activity � so high rT3 levels can give you signs of hypothyroidism even though the other thyroid hormones are in the "normal range".

What Is Reverse T3?

Why is this a potential problem? Reverse T3 can bind to a cell in the same way T3 does, except when reverse T3 binds to it, nothing happens. When this happens, Dr. Rose explains, “reverse T3 and T3 will then compete for receptors' at the cellular level. Your body can start showing symptoms of hypothyroidism when not enough T3 is binding to your cells.”