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Reverse T3

Thyroid hormones are essential in maintaining and regulating the body's metabolism.  Triiodthyronine (T3) is the most active of the thyroid hormones. 

Approximately 85% of circulating T3 is produced by mono deiodination of thyroxine (T4) in tissues such as the liver, muscle and kidney.  Selenium and zinc are required for this process.


Reverse T3

Reverse T3 (rT3) is an inactive form of T3 that is produced in the body particularly during periods of stress.  rT3 differs from T3 in that the missing deiodinated iodine is from the inner ring of the thyroxine molecule compared with outer ring on T3.  Under normal conditions T4 will convert to both T3 and rT3 continually and the body eliminates rT3 quickly.  Under certain conditions, more rT3 is produced and the desirable conversion of T4 to T3 decreases. This occurs during fasting, starvation, illness such as liver disease and during times of increased stress.

This becomes a vicious cycle as rT3 competes with T3 as a substrate for the 5-deiodinase enzyme. This inhibits the conversion of T4 to T3, with more T4 being converted to more rT3.  An increased production of rT3 is often seen in patients with disorders such as fibromyalgia, chronic fatigue sydrome (CFS), Wilson’s Thyroid Syndrome and stress. Measurement of rT3 is also valuable in identifying sick euthyroid syndrome where active T3 is within normal range and rT3 is elevated.



 Test Results Aetiology
 Increased rT3    

 - Increased Cortisol and other stressors

 - Increased Adrenalin

 - Wilson's Thyroid Syndrome (excessive production of rT3 from T4)

 - Euthyroid Sick Syndrome (Low circulating T3 levels in spite of normal gland function)

 - Common in Chronic Fatigue Syndrom (CFS) and fibromyalgia

 - Decreased levels of Selenium



Patient Preparation

Patients does not require any specific preparation before having blood collected


Turnaround Time

Test results are usually available within 10-14 working days.


Test Results

Patient results are delivered via electronic download unless requested otherwise. Results can also be issued via hardcopy, fax or web based e-viewer.


Technical Support

All Australian Clinical Labs Functional Pathology tests are accompanied by an Interpretive Guide to assist practitioners in their clinical understanding and patient management for each result. Australian Clinical Labs Functional Pathology also has experienced full time Technical Advisors available for practitioners to discuss appropriate test selection, interpretation of test results, individual cases and other technical matters. Please call 1300 55 44 80 between the hours of 9:00am and 5:00pm  AEST or email csfp@AustralianClinicalLabs.com.au