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Test Code RT3 T3 (Triiodothyronine), Reverse, Serum

Important Note

Beaker/EPIC order code is LAB1230179

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

T3 (Triiodothyronine), Reverse, S

Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 0.8 mL

Reject Due To



Mild OK; Gross reject


Mild OK; Gross OK


Mild OK; Gross OK



Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 28 days
  Ambient  28 days
  Frozen  28 days

Specimen Minimum Volume

0.4 mL

Day(s) and Time(s) Performed

Monday, Wednesday, Thursday, Friday; 9 a.m.

Specimen Retention Time

14 days

Analytic Time

2 days

Reference Values

10-24 ng/dL

Useful For

An aid in the diagnosis of the "sick euthyroid" syndrome

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Portions of this test are covered by patents held by Quest Diagnostics.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
RT3 T3 (Triiodothyronine), Reverse, S 3052-8


Result ID Test Result Name Result LOINC Value
9405 T3(Triiodothyronine),Reverse,S 3052-8

Clinical Information

Reverse triiodothyronine (rT3) differs from triiodothyronine (T3) in the positions of the iodine atoms attached to the aromatic rings. The majority of rT3 found in the circulation is formed by peripheral deiodination (removal of an iodine atom) of T4 (thyroxine). rT3 is believed to be metabolically inactive.


The rT3 level tends to follow the T4 level: low in hypothyroidism and high in hyperthyroidism. Additionally, increased levels of rT3 have been observed in starvation, anorexia nervosa, severe trauma and hemorrhagic shock, hepatic dysfunction, postoperative states, severe infection, and in burn patients (ie, "sick euthyroid" syndrome). This appears to be the result of a switchover in deiodination functions with the conversion of T4 to rT3 being favored over the production of T3.


In hospitalized or sick patients with low triiodothyronine (T3) values, elevated reverse triiodothyronine (rT3) values are consistent with "sick euthyroid" syndrome. Also, the finding on an elevated rT3 level in a critically ill patient helps exclude a diagnosis of hypothyroidism.


The rT3 is high in patients on medications such as propylthiouracil, ipodate, propranolol, amiodarone, dexamethasone, and the anesthetic agent halothane. Dilantin decreases rT3 due to the displacement from thyroxine-binding globulin, which causes increased rT3 clearance.


To convert from ng/dL to nmol/L, multiply the ng/dL result by 0.01536.


Generally, reverse triiodothyronine tests are not necessary since triiodothyronine should not be ordered in hospitalized or sick patients.

Clinical Reference

Moore WT, Eastman RC: Diagnostic Endocrinology. St. Louis, Mosby, 1990, pp 182-183

Method Description

Reverse triiodothyronine-13C (rT3-13C) is added to serum or plasma samples as an internal standard. Reverse T3 (rT3) and rT3-13C are dissociated with a protein precipitation and then extracted from the specimens using a solid-phase cartridge. The eluate is dried down under nitrogen, reconstituted with mobile phase and analyzed by liquid chromatography-tandem mass spectrometry using multiple reactions monitoring in the positive mode.(Zhang Y, Conrad AH, Conrad GW: Detection and quantification of 3, 5, 3'-triiodothyronine and 3, 3', 5'-triiodothyronine by electrospray ionization tandem mass spectrometry. J Am Soc Mass Spectrom 2005 Nov;16[11]:1781-1786)


If not ordering electronically, complete, print, and send a General Request Form (T239) with the specimen (