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FT3 : rT3


The rT3 ratio measures the level of reverse T3 in relation to free T3 in the blood. The body converts T4 into both T3 and rT3 in varying proportions in order to regulate the metabolism. Reverse T3 can be elevated when the body needs to conserve energy and higher levels have been found in people on restricted calorie diets and people with liver disease, pulmonary disease, diabetes and heart failure. Research into rT3 is very limited and currently only exists within an intensive care setting. Some practitioners believe it plays a role in the management of a thyroid condition, but so far, there is very little evidence to support that view.

What might a low result mean?

A low FT3:rT3 ratio is thought to mean that your body is producing more rT3 in order to conserve energy to fix a problem. The ratio in itself will not help identify what that problem is, but it may indicate that an underlying condition may need more careful management.

How might I improve my result?

You may be able to improve your rT3 ratio by taking steps to improve your general health. This means eating a nutritionally rich diet and avoiding yoyo dieting if you are trying to lose weight. Taking steps to control stress through relaxation techniques and regular sleep may also help.

You may find practitioners who will prescribe T3 (liothyronine) to improve your symptoms. Please bear in mind that for the majority of people studies show that there is no benefit to taking T3 instead of levothyroxine. People who are struggling to control their thyroid symptoms with levothyroxine alone may experience an improvement when taking T3, however, this needs to be started by a specialist, carefully monitored and managed to make sure that you don’t take more thyroid hormone than you need.