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24907 T3 Reverse (RT3)

T3 Reverse (RT3)
Test Code: T3RSO
Synonyms/Keywords
Triiodothyronine, Reverse
Useful For
A​ids in the diagnosis of the sick euthyroid syndrome
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
No​ ​Serum ​Red Top Tube (RTT) ​Serum Separator Tube (SST) ​0.8 mL ​0.4 mL
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​ ​ Refrigerate (preferred) 28 days
​Ambient 28 days
Frozen ​28 days
Rejection Criteria
Gross Hemoysis
Interference

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

Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories​ Monday through Friday​ ​2-6 days ​LC-MS/MS
Reference Lab
Test 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.

Reference Range Information
Performing Location Reference Range
​Mayo Clinic Laboratories ​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.

Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​84482
Synonyms/Keywords
Triiodothyronine, Reverse
Ordering Applications
Ordering Application Description
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
No​ ​Serum ​Red Top Tube (RTT) ​Serum Separator Tube (SST) ​0.8 mL ​0.4 mL
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​ ​ Refrigerate (preferred) 28 days
​Ambient 28 days
Frozen ​28 days
Rejection Criteria
Gross Hemoysis
Interference

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

Useful For
A​ids in the diagnosis of the sick euthyroid syndrome
Reference Range Information
Performing Location Reference Range
​Mayo Clinic Laboratories ​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.

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories​ Monday through Friday​ ​2-6 days ​LC-MS/MS
Reference Lab
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​84482
For most current information refer to the Marshfield Laboratory online reference manual.