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HelpTest Code RT3 T3 (Triiodothyronine), Reverse, Serum
Reporting Name
T3 (Triiodothyronine), Reverse, SUseful For
Aiding 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.
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 0.8 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
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 |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Gross icterus | OK |
Reference Values
10-24 ng/dL
Day(s) Performed
Monday through Friday
CPT Code Information
84482
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.
Interpretation
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.
Cautions
Generally, reverse triiodothyronine tests are not necessary since triiodothyronine should not be ordered in hospitalized or sick patients.
Method Description
Reverse T3-carbon 13 is added to serum samples as an internal standard. Reverse T3 (RT3) and RT3-carbon 13 are dissociated with a protein precipitation and then extracted from the specimens using a solid phase extraction. The eluate is dried down under nitrogen, reconstituted with mobile phase and analyzed by liquid chromatography tandem mass spectrometry using multiple reaction monitoring in the positive mode.(Unpublished Mayo Method)