What is Reverse T3 (rT3)?

Reverse T3 (rT3) is a biomarker in the blood that represents an inactive form of the thyroid hormone triiodothyronine (T3). It is produced as a byproduct of the normal metabolism of T3 and plays a role in the regulation of thyroid function.

Why should you test for Reverse T3 (rT3)?

Testing rT3 can be useful for assessing thyroid function, especially in complex cases where standard thyroid function tests, such as TSH and T4, do not provide a clear picture. It is helpful in the evaluation of patients with symptoms of hypothyroidism or hyperthyroidism, particularly when these symptoms persist despite normal test results.

What does it indicate?

rT3 levels provide insight into how the body regulates energy balance and metabolism. An abnormality of the normal rT3 value can indicate a disruption in thyroid function or an adjustment of the body to specific health conditions, such as severe illness or stress.

What does a high rT3 level mean?

A high level of rT3 may indicate a condition called "Low T3 Syndrome" or a non-thyroidal illness, where there is an increased conversion of T3 to rT3. This may point to suppressed thyroid function or a reaction of the body to physical stress, starvation, infection, or other metabolic stressors.

What does a low rT3 level mean?

A low level of rT3 is less common and may indicate hyperthyroidism or an excessively active thyroid function. It can also point to insufficient production of thyroid hormones due to various causes.