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Test Code RT3 T3 (Triiodothyronine), Reverse, Serum

Reporting Name

T3 (Triiodothyronine), Reverse, S

Useful For

Aiding in the diagnosis of the sick euthyroid syndrome

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 0.8 mL

Specimen Minimum Volume

0.4 mL

Specimen Stability Information

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

Reference Values

10-24 ng/dL

Day(s) and Time(s) Performed

Monday through Friday; 10 a.m.

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 Reference

1. Bowerbank SL, Carlin MG, Dean JR: A direct comparison of liquid chromatography-mass spectrometry with clinical routine testing immunoassay methods for the detection and quantification of thyroid hormones in blood serum. Anal Bioanal Chem. 2019 May;411(13):2839-2853

2. Moore WT, Eastman RC: Diagnostic Endocrinology. Mosby; 1990:182-183

Method Description

Reverse triiodothyronine-13C (rT3-13C) is added to patient sample as an internal standard. 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; Sakai H, Nagao H, Sakurai M, et al. Correlation between serum levels of 3,3',5'-triiodothyronine and thyroid hormones measured by liquid chromatography-tandem mass spectrometry and immunoassay PLoS One. 2015;10[10]:e0138864. doi: 10.1371/journal.pone.0138864. Erratum in: PLoS One. 2016;11[7]:e0159169)

Analytic Time

2 days

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus OK

Method Name

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

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


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