Triiodothyronine (T3), Reverse

Abbrev Code:T3REV   
Order Code:LAB138Order Name:T3 Reverse
Synonyms:Reverse T3; T3, Reverse
Methodology:Tandem mass spectrometry/Liquid chromatography
CPT Codes: 84482 x1
Turnaround Time:Specimens are sent to reference laboratory Mon-Sat; results are reported in 1-4 days.

For tests developed and validated by ARUP (previously referred to as Compliance Statement B, C or D). This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the U.S. Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Collection Instructions

Optimal Volume:4 mL
Minimum\Peds Volume:2.2 mL
Container:Red or gold (gel)
Alternate Containers: Purple (EDTA), Red (no gel)
Causes for Rejection:Gross hemolysis.

Processing and Shipping

Specimen Processing:Allow sample to clot at room temperature. Centrifuge and aliquot within 2 hours of collection 2 mL, 1 mL minimum. Samples are stable refrigerated for 7 days.
Shipping Instructions:Ship on dry ice.
Test Performed at or Referral Lab Lab Sendouts  (ARUP)
Referral Lab number:2007918


Reference Range:

0-17 y

Not established

18 y and older

9.0-27.0 ng/dL




Reverse T3 (rT3) differs from thyroid hormones in that it has no effect on metabolic rate and indeed may be a waste product. Patients with abnormalities of energy metabolism may also show significant variations in serum rT3 levels. Caloric deprivation (fasting) usually results in higher concentrations of rT3, as do various systemic diseases involving fever. This appears to result from the conversion of T4 to rT3 being favored at the expense of T3 production. Hence, rT3 measurements may be useful in the diagnosis of the “sick euthyroid” syndrome. Most drugs that affect thyroid function also change rT3 levels.


Disorders associated with increased rT3 values include:

·          Hyperthyroidism

·          Systemic febrile illnesses

·          Administration of amiodarone

·          Fasting

·          Administration of radiographic contrast agents


Disorders associated with decreased rT3 values include:

·          Hypothyroidism

·          Administration of estrogens or progestogens

·          Administration of corticosteroids

·          Administration of anti-thyroid drugs



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