T3 (Triiodothyronine) Reverse (Sendout)

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General Information

Lab Name
Lab Code
512
External Test Id
RT3
Description

Useful For: Aiding in the diagnosis of the sick euthyroid syndrome.

***Notification: Effective 04/07/26, the RT3 test is offline at Mayo due to performance issues. Samples will be temporarily forwarded to Quest Diagnostics for alternative test T3 Reverse, LC/MS/MS.***

References
Synonyms
Reverse T3, RT3, Triidothyronine Reverse
Components

Interpretation

Method

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

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

Reference Range
Ref. Range Notes

Quest Reference Range (Temporary Referral): 8-25 ng/dL

Reference Range (Mayo):

Reference Interval: 10-24 ng/dL

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.

Interferences and Limitations

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

References

Ordering & Collection

Specimen Type
Blood
Collection

3 mL blood in RED TOP tube or GOLD SST

Handling Instructions

Outside Laboratories: Centrifuge sample and aliquot serum into a separate plastic vial. Freeze serum at -20°C while awaiting shipment. Transport on dry ice.

Stability: Frozen (preferred): 30 days; Refrigerated: 7 days; Ambient: 7 days.

Quantity
Requested: 0.5 mL serum
Minimum: 0.3 mL serum

Processing

Receiving Instructions

Centrifuge sample and aliquot serum into a separate plastic vial. Freeze serum at -20°C.

Login: SEND1-;FREEZE SERUM

  • RSNDT1: MAYNIC
  • RSTYP1: SRM
  • RTSRQ1: ;Reverse T3 (Mayo Test FRT3S)

Sendouts:

  • Order Mayo Test: FRT3S

Stability: Frozen (preferred): 30 days; Refrigerated: 7 days; Ambient: 7 days.

Misc Sendout

Performance

Lab Department
Frequency
Performed: Daily. Reported: 4-8 days from sample receipt at Mayo Clinic Labs.
Available STAT?
No
Performing Location(s)
Sendout Mayo forwards to Quest Diagnostics Nichols Institute
800-533-1710

33608 Ortega Highway
San Juan Capistrano, CA 92675

Billing & Coding

Billing Comments

CPT: 84482