What causes high Reverse T3?

Elevated rT3 can result from chronic stress, severe calorie restriction, illness, inflammation, liver or kidney disease, certain medications (beta-blockers, amiodarone), and high cortisol. The body produces more rT3 to slow metabolism during these states.

Is Reverse T3 testing standard?

Reverse T3 testing is not routinely recommended by mainstream endocrinology organizations and may not be covered by insurance. It is more commonly used in functional medicine. Some practitioners find it valuable; others consider it unnecessary.

Can I lower my Reverse T3?

Addressing underlying causes helps: reducing stress, adequate calorie intake, treating illness, improving sleep, and managing inflammation. Some practitioners add T3 medication for persistent elevation, though this is controversial.

What is the Free T3:Reverse T3 ratio?

This ratio compares active T3 to inactive rT3. A higher ratio suggests good T4-to-T3 conversion; a lower ratio suggests shunting to rT3. Calculation depends on units used. Discuss interpretation with your provider.

🦋 Thyroid

Reverse T3 Blood Test

Name: Reverse T3 Blood Test
Brand: Justlabs
SKU: 0090963
Price: 28 USD
Availability: InStock

Reverse T3

Reverse T3 (rT3) is an inactive form of thyroid hormone produced when the body diverts T4 conversion away from active T3. Elevated levels may indicate stress, illness, or thyroid conversion problems.

Reverse T3 (rT3) is a metabolically inactive form of thyroid hormone. Your body normally converts T4 (the storage hormone) into T3 (the active hormone), but under certain conditions, it instead converts T4 into rT3, which blocks T3 receptors without activating them.

This "thyroid shunting" is a protective mechanism during illness, stress, or calorie restriction—slowing metabolism to conserve energy. However, chronically elevated rT3 can cause hypothyroid symptoms despite normal TSH and T4 levels.

Reverse T3 testing is controversial in mainstream medicine but valued in functional medicine for explaining persistent hypothyroid symptoms with normal conventional labs. The ratio of Free T3 to Reverse T3 may be more informative than rT3 alone.

Price

$28

Results

3-5 days

Lab Network

Quest

Fasting

Not Required

What's Measured

Reverse T3

What This Test Measures

This test measures the concentration of Reverse T3 in your blood, reported in ng/dL. It's often interpreted alongside Free T3 to calculate the Free T3:Reverse T3 ratio.

Who Should Consider This Test

People with hypothyroid symptoms despite normal TSH, those with chronic illness or stress, anyone investigating "low T3 syndrome," people on T4-only thyroid medication with persistent symptoms, and those evaluating thyroid conversion issues.

Health Insights

Conditions Screened

Low T3 syndromeEuthyroid sick syndromeThyroid conversion problemsChronic stress effectsRecovery from illnessCalorie restriction effects

Related Symptoms

Fatigue despite normal TSHCold intoleranceWeight gainBrain fogDepressionHair lossConstipationMuscle weakness

When to Get Tested

No fasting required. Best tested alongside Free T3 and Free T4 for complete interpretation. Avoid testing during acute illness unless evaluating sick euthyroid syndrome.

Understanding Your Results

Normal Reverse T3: 9-27 ng/dL. More important is the Free T3:Reverse T3 ratio. Ratios above 20 (when Free T3 is in pg/mL and rT3 in ng/dL) are generally considered optimal. Lower ratios suggest T4-to-rT3 shunting.

What to Expect

After placing your order, you'll receive an email from Rupa Health (our lab order partner) within 24 business hours to sign a consent form and schedule your blood draw at a Quest Diagnostics location.

The blood draw typically takes just a few minutes. Results are usually available within 3-5 business days and will appear in your secure Justlabs dashboard.

Our results include reference ranges and easy-to-understand indicators showing whether your values are within normal limits.