Reverse T3 Testing in Thyroid Treatment

What You Should Know

Reverse T3 RT3 thyroid testing
RapidEye / Getty Images

The issue of measuring Reverse T3 (RT3)—also known as reverse triiodothyronine—is controversial in the thyroid community. The conventional endocrinology for the most part dismisses the value of RT3 measurement in diagnosing, treating, and managing hypothyroidism. At the same time, the integrative and holistic medical community, and in particular those physicians who focus on optimal hormone balance, consider measuring RT3 to be essential in the diagnosis and management of an underactive thyroid.

Let's take a look at RT3, what it is, and how integrative physicians are using this test to detect subtle imbalances in the thyroid.

What Is Reverse T3?

RT3 is a metabolite of T4 (thyroxine). Typically, when T4 loses an atom of iodine—a process known as monodeiodination, or T4 to T3 conversion—it becomes triiodothyronine (T3), the active thyroid hormone. But in some cases, the body conserves energy by converting the T4 instead into RT3, an inactive form of T3 that is incapable of delivering oxygen and energy to the cells, as T3 does.

Measuring Reverse T3

RT3 can be measured by a blood test. This can be ordered by a physician, or in most states in the United States, can also be ordered without a physician's lab order by using a direct-to-consumer laboratory testing service.

Elevated RT3 as Evidence of Hypothyroidism

As mentioned, conventional endocrinology assumes that in most people, the T4 to T3 conversion process functions seamlessly and that the presence of elevated RT3 is not evidence of any thyroid dysfunction.

Integrative hormone experts, however, have a different view of the role and value of RT3. Some integrative physicians believe that elevated levels of RT3—even though TSH, Free T3 and Free T3 values may be within the normal reference range—reflect a thyroid problem at the cellular level—a condition that Kent Holtorf, MD calls "cellular hypothyroidism."

In this integrative view, elevated RT3 can be triggered by ongoing chronic physical or emotional stress, adrenal fatigue, low ferritin (stored iron) levels, acute illness and injury, and chronic disease, among other factors.

According to Dr. Holtorf:

Reverse T3 is actually an "antithyroid"—T3 is the active thyroid that goes to the cells and stimulates energy and metabolism. Reverse T3 is a mirror image—it actually goes to the receptors, sticks there, and nothing happens. So, it blocks the thyroid effect. Reverse T3 is kind of a hibernation hormone, in times of stress and chronic illness, it lowers your metabolism. So, many people seemingly have normal thyroid levels, but if they have high Reverse T3, they're actually suffering from hypothyroidism.

A study in The Journal of Clinical Endocrinology & Metabolism found that TSH and/or T4 levels can be poor indicators of the actual thyroid levels in tissues, and therefore, in a substantial percentage of patients, do not reflect whether or not a person has truly normal thyroid levels. This study showed that increased T4 and RT3 levels, along with decreased T3 levels, are associated with symptomatic hypothyroidism at the cellular or tissue level.

The authors of this study concluded:

Subjects with low T3 and high reverse T3 had the lowest PPS [a score that evaluates normal activities and measures physical and mental functioning]...subjects with high reverse T3 concentrations had worse physical performance scores and lower grip strength. These high RT3 levels were accompanied by high FT4 levels (within the normal range)…These changes in thyroid hormone concentrations may be explained by a decrease in peripheral thyroid hormone metabolism…

According to Kent Holtorf, MD, a Reverse T3 level above 150—or a Free T3/Reverse T3 ratio that exceeds .2 [when the Free T3 is measured in picograms per milliliter (pg/mL)]—may indicate hypothyroidism.

Says Dr. Holtorf:

A high reverse T3 demonstrates that there is either an inhibition of reverse T3 uptake into the cell and/or there is increased T4 to reverse T3 formation. …reverse T3 is an excellent marker for reduced cellular T4 and T3 levels not detected by TSH or serum T4 and T3 levels. …high or high normal RT3 is not only an indicator of tissue hypothyroidism but also that T4 only replacement would not be considered optimal in such cases and would be expected to have inadequate or sub-optimal results.

Treating Elevated Reverse T3

According to integrative practitioners, one of the key ways to address elevated RT3 and "cellular hypothyroidism" is through thyroid treatment with a medication that contains T3.

One preferred form is time-released T3. Time-released T3 is a compounded form of T3 available by prescription. In some cases, this T3 is prescribed as a stand-alone thyroid treatment.

In other cases, T3 is added to a synthetic T4 prescription drug (i.e., Synthroid, Unithroid, Tirosint), or a prescription natural desiccated thyroid drug (i.e., Nature-throid, Armour) is prescribed.

Reverse T3: The Challenge

Patients who are interested in RT3 testing may be challenged to find a physician willing to run the tests, or treat any imbalances. Endocrinologists, many of whom do not test T3, RT3, or prescribe T3 medications, may not be a good choice for those patients. Instead, an integrative physician, holistic MD, or physician with expertise in hormone balance may be needed.

Holistic gynecologist and hormone expert Sara Gottfried, MD, author of The Hormone Cure, has integrated Reverse T3 testing into her practice.

I used to order Reverse T3 in a patient if I'd optimized the TSH and Free T3 but the patient still had hypothyroidism symptoms, but now I order it more often at the start, because I think it's informative in deciding about the formulation. For example, if a patient has high Reverse T3, I'm more likely to use the compounded, time-released T3 as part of their treatment.


National Academy of Hypothyroidism,
Van den Beld, Annewieke. Thyroid Hormone Concentrations, Disease, Physical Function and Mortality in Elderly Men. The Journal of Clinical Endocrinology & Metabolism, 2005; 90(12):6403-6409