Reverse T3 (rT3) test

Reverse T3 (rT3) is a byproduct of thyroid hormone metabolism. This test is generally not recommended for routine thyroid disease evaluation.

When should you test for reverse T3?

The rT3 test can be useful in certain cases. Sometimes people with normal TSH and free T4 levels still experience hypothyroid symptoms such as fatigue, depression, or weight gain. If you experience chronic stress, depression, brain fog, anxiety, weight fluctuations, or hair loss, your doctor may recommend this test.

Optimal results for the reverse T3 test:

Optimal result: 9.2–24.1 ng/dL or 141.32–370.20 pmol/L.

What does an elevated reverse T3 level mean?

Elevated rT3 levels can be caused by almost any serious or chronic illness. For example, low blood oxygen levels significantly increase rT3 levels in the serum. People with severe malnutrition (especially carbohydrate deficiency), severe diabetes, kidney or liver disease may also have elevated rT3 levels.

Can high reverse T3 levels cause high blood pressure?

Excess rT3 itself is usually not a direct cause of high blood pressure. However, excess active T3 (triiodothyronine) can lead to metabolic and hemodynamic changes: increased metabolic rate, cardiac preload, and ventricular contractility, and decreased systemic vascular resistance, causing increased cardiac output and hypertension. These changes can also affect rT3 levels in the body.

The reverse T3 test is not a standard test for all patients, but it can be useful for diagnosing those who experience hypothyroid symptoms despite normal results from other thyroid hormone tests. Discuss with your doctor whether this test is suitable for you, especially if you have chronic conditions or symptoms that are difficult to explain.