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HelpTest Code LAB138 T3 (Triiodothyronine), Reverse, Serum
Additional Codes
RT3
Useful For
Aiding in the diagnosis of the sick euthyroid syndrome
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.
On-campus collections: Tube to 99 or deliver to University Extension Hospital Room EH318. Submission Container/Tube: Plastic vial, Refrigerated
Off-campus collections: Centrifuge and aliquot within 2 hours. Specimen to be stored/transported Refrigerated.
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) 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 |
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.
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and analyzed by liquid chromatography tandem mass spectrometry using multiple reaction monitoring in the positive mode.(Unpublished Mayo Method)
Report Available
2 to 6 daysSpecimen Retention Time
14 daysReject 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.
Forms
If not ordering electronically, complete, print, and send a General Request (T239) with the specimen.