Reverse T3 (rT3)

Reverse T3 (rT3) is an underutilized test in conventional medicine. It is considered an "inactive" thyroid hormone, although updated research shows that it inhibits other thyroid hormones. In this article, I'll discuss the rT3 test, how pregnancy affects blood results, and common causes of abnormal findings. 

rT3 Testing

Reverse T3 (rT3) measures the amount of rT3 in the bloodstream. 

​The conversion of T4 to rT3 is considered an adaptive mechanism in response to certain conditions such as stress, illness, or changes in thyroid hormone levels. Measuring rT3 can help assess cellular function and utilization of thyroid hormones.

rT3 in Pregnancy

​Increasing cortisol levels reduces serum-free T4 and T3 while increasing rT3. In the first trimester, rT3 increases significantly, decreasing slightly and plateauing in the second trimester, then increasing again in the third trimester.

This is also driven by the placenta's increased production of deiodinase 3 enzymes. 

High rT3 in Pregnancy

There is limited data on the consequences of high rT3 in pregnancy. 

Most Common Causes of High rT3 in Pregnancy

• Chronic Stress
• Inflammation/Illness
• Overmedication
• Hyperthyroidism
• Vitamin A Deficiency
• Environmental Toxin Exposure 
• Oxidative Stress

Low rT3 in Pregnancy

There is limited data on the consequences of low rT3 in pregnancy. 

Most Common Causes of Low rT3 in Pregnancy

• Fasting
• Malnutrition
• Hypothyroidism

Curious About Thyroid Hormone Testing in Pregnancy?

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Medical Disclaimer:
This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.​

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