Free T3 : Reverse T3 Ratio


Free T3:Reverse T3 Ratio – an interview with Dr. Shawn Soszka, Naturopathic Physician and Acupuncturist

Dr. Shawn Soszka is a Naturopathic Physician and acupuncturist practicing in Portland, OR. He is the author of “The Thyroid Fix” and an expert in thyroid assessment and thyroid dysfunction.

Dr. Soszka and Dr. Weatherby talk about the Free T3:Reverse T3 ratio in the video above and discuss its uses in clinic.

The Free T3: Reverse T3 ratio is now being automatically calculated by the Optimal DX software if both the Free T3 and Reverse T3 are added into the system.

The Ratio

The Free T3 to Reverse T3 ratio is used to determine whether there are issues with thyroid hormone conversion. A high or optimal ratio of Free T3 to Reverse T3 isn’t considered clinically significant. A low Free T3 to Reverse T3 is a sign of Thyroid Hormone Conversion Syndrome, a situation where the peripheral conversion of T4 into the more metabolically active T3 is decreased.

The ratio of Free T3 to Reverse T3 can tell you what’s happening at the tissue level because it helps determine how effective thyroid conversion from T4 into active T3 really is.

Production of Reverse T3, a non-metabolically active form of thyroid hormone, often increases during times of stress such as severe trauma; shock; surgery; severe infection or burns; critical illness; liver dysfunction; starvation; anorexia nervosa; and chronic stress. The phenomenon of increased Reverse T3 without the presence of thyroid disease may be referred to as “sick euthyroid” syndrome or “non-thyroidal illness.”  

In such cases, there is less conversion of T4 to T3 in the liver. Instead, there is increased conversion of T4 to T3 in the periphery… peripheral production of T3 yields more Reverse T3. This action is believed to reduce metabolic activity and conserve energy as the body fights the stressor.

As production of Reverse T3 increases, levels of metabolically active T3 can decline, creating a decrease in the ratio of Free T3 to Reverse T3. It is important to recognize that these changes may be due to factors other than thyroid disease and may not require thyroid medication.

Many Functional Medicine practitioners are in agreement that a Free T3 to Reverse T3 ratio of > 20 is ideal. This is basically saying that you want at least 20 times as much Free T3 to Reverse T3 to be in the best health. However, if Free T3 is elevated then this can make the ratio look healthier than it is. This is seen in people taking T3 medication.

Some practitioners say anything over 2 is optimal but a ratio between 10 – 20 is preferable with a value > 20 being ideal.

Calculating The Ratio

Good news! The Free T3: Reverse T3 ratio is now being automatically calculated by the Optimal DX software if both the Free T3 and Reverse T3 are added into the system. No need to do any conversions as the software will do this for you and will now show the result in the Blood Test Results Report:



However, if you simply want to do the calculation manually then please follow these instructions:

  1. First off, the Free T3 must be in the pg/dl unit, i.e. in the hundreds, and not in pg/ml.

  2. If the Free T3 is in the pg/ml unit, you must multiply the result by 100 to convert pg/ml into pg/dl i.e 3.25 pg/ml = 325 pg/dl

  3. The Reverse T3 must be in ng/dl (normal unit in U.S.) i.e. 17 ng/dl

  4. The ratio is calculated by dividing the Free T3 result by the Reverse T3 result, i.e. 325 / 17 = 19.
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