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Reverse Triiodothyronine (rT3)

What is Reverse T3 (rT3)?

Reverse T3 (rT3) is a thyroid hormone produced when the body converts the more active hormone, triiodothyronine (T3), into an inactive form. While T3 actively regulates metabolism and energy production, rT3 does not exert metabolic effects and is considered biologically inactive.

Role of Reverse T3 in the Body

The body increases rT3 production in response to stress, illness, or caloric restriction. This is believed to be a protective adaptation, helping to slow down metabolism and conserve energy during times of physical strain. Although this mechanism can be beneficial short-term, persistently high rT3 levels may signal underlying thyroid dysfunction or chronic illness.

When is Reverse T3 Testing Useful?

A reverse T3 blood test is useful in evaluating complex thyroid-related symptoms, especially when standard thyroid tests (TSH, free T3, and free T4) appear normal, yet patients still experience:

Fatigue

Weight gain

Low body temperature

Poor concentration

In such cases, elevated rT3 may be contributing to symptoms of functional hypothyroidism or non-thyroidal illness.

Comprehensive Thyroid Evaluation

Because interpreting rT3 levels alone can be misleading, it is essential to assess them alongside other key markers such as:

Thyroid-Stimulating Hormone (TSH)

Free T3

Free T4

This combined approach provides a clearer picture of thyroid function and helps healthcare professionals tailor treatment effectively.

Reverse T3 Testing in Slough

For residents in Slough and the surrounding Berkshire areas, reverse T3 testing is available as part of advanced thyroid health screening. If you are experiencing unexplained fatigue, weight issues, or other symptoms despite normal thyroid results, a comprehensive thyroid panel including rT3 may uncover hidden imbalances and guide more accurate diagnosis and care.

There is an additional £25 phlebotomy fee for every donation.