Doctor's Assessment Included
Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Reverse T3
Reverse T3 is an inactive thyroid hormone that may increase during overtraining, underfuelling, or physical stress. For athletes, elevated levels might indicate the body is conserving energy by reducing active thyroid hormone availability.
Reference Ranges
Low
0.14
Normal
0.54
High
Low
0.14
Normal
0.54
High
Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.
What It Measures
This test measures the level of reverse triiodothyronine (rT3) in your blood. Reverse T3 is produced when the body converts T4 into an inactive form instead of active T3. It may serve as an indicator of how your body is prioritising thyroid hormone utilisation.
Why It Matters
For athletes, elevated Reverse T3 may signal that the body is under excessive training stress or caloric deficit. Some sports medicine providers use it to detect early signs of overtraining syndrome. Addressing elevated levels might help restore performance and recovery capacity.
When to Test
Some people may consider testing Reverse T3 when experiencing persistent fatigue or symptoms of low thyroid function despite normal TSH and T4 levels. It might be useful during periods of chronic stress or illness. Your healthcare provider can advise on whether this test is appropriate.
Symptoms
Low Levels
Low Reverse T3 levels are less commonly discussed, but some healthcare providers note that very low levels may occasionally be seen alongside hyperthyroid states. Symptoms might overlap with those of an overactive thyroid. Discuss any concerns with your healthcare provider.
High Levels
Some people with elevated Reverse T3 levels may experience fatigue, brain fog, weight gain, or cold intolerance despite normal T4 and TSH readings. High levels might suggest the body is under significant physiological stress. Your healthcare provider can help interpret these results.
Lifestyle Tips
Some people may help support healthy Reverse T3 levels by managing chronic stress, avoiding extreme caloric restriction, and prioritising sleep. Adequate nutrition with sufficient iron and selenium might also play a role. Always consult your healthcare provider before making changes.
Frequently Asked Questions
What causes Reverse T3 to become elevated?
Elevated Reverse T3 may result from chronic stress, severe illness, caloric restriction, or inflammation. Some healthcare providers suggest the body produces more Reverse T3 as a protective mechanism to slow metabolism during challenging periods.
Is Reverse T3 testing routinely recommended?
Reverse T3 is not typically part of standard thyroid panels. It is sometimes ordered when a healthcare provider suspects a conversion issue or when symptoms persist despite normal TSH and Free T4 levels. Your provider can determine if it is appropriate for you.
Can dieting increase Reverse T3 levels?
Some research suggests that significant caloric restriction or prolonged dieting may increase Reverse T3 levels as the body attempts to conserve energy. This is sometimes referred to as adaptive thermogenesis. Discuss dietary concerns with your healthcare provider.