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Test Code LAB1399 T3 (Triiodothyronine), Total, Serum

Additional Codes

 

Test Name in EPIC EPIC Test Code Mnemonic Mayo Test ID
T3 (TRIIODOTHYRONINE) TOT LAB1399 T3TOT T3

 

Reporting Name

T3 (Triiodothyronine), Total, S

Useful For

Second-order testing for hyperthyroidism in patients with low thyroid-stimulating hormone values and normal thyroxine levels

 

Diagnosis of triiodothyronine toxicosis

Testing Algorithm

See Thyroid Function Ordering Algorithm in Special Instructions.

Method Name

Electrochemiluminescence Immunoassay

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Additional Information: 12 hours before this blood test do not take multivitamins or dietary supplements containing biotin or vitamin B7, which are commonly found in hair, skin, and nail supplements and multivitamins.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Frozen  30 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross OK

Icterus

Mild OK; Gross OK

Other

NA

Reference Values

Pediatric

0-5 days: 73-288 ng/dL

6 days-2 months: 80-275 ng/dL

3-11 months: 86-265 ng/dL

1-5 years: 92-248 ng/dL

6-10 years: 93-231 ng/dL

11-19 years: 91-218 ng/dL

 

Adult (≥20 years): 80-200 ng/dL

 

For SI unit Reference Values, see https://www.mayomedicallaboratories.com/order-tests/si-unit-conversion.html.

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-12 a.m.

Saturday; 6 a.m.-6 p.m.

CPT Code Information

84480

LOINC Code Information

Test ID Test Order Name Order LOINC Value
T3 T3 (Triiodothyronine), Total, S 3053-6

 

Result ID Test Result Name Result LOINC Value
T3 T3 (Triiodothyronine), Total, S 3053-6

Interpretation

Triiodothyronine (T3) values >200 ng/dL in adults or > age related cutoffs in children are consistent with hyperthyroidism or increased thyroid hormone-binding proteins.

 

Abnormal levels (high or low) of thyroid hormone-binding proteins (primarily albumin and thyroid-binding globulin) may cause abnormal T3 concentrations in euthyroid patients.

Cautions

Twelve hours before this blood test do not take multivitamins or dietary supplements containing biotin or vitamin B7, which are commonly found in hair, skin, and nail supplements and multivitamins.

 

Triiodothyronine (T3) is not a reliable marker for hypothyroidism.

 

T3 is not useful for general screening of the population without a clinical suspicion of hyperthyroidism. Therapy with amiodarone can lead to depressed T3 values.

 

Phenytoin, phenylbutazone, and salicylates cause release of T3 from the binding proteins, thus leading to a reduction in the total T3 hormone level at normal free T3 levels.

 

Autoantibodies to thyroid hormones can interfere with the assay.

 

Binding protein anomalies may cause values that deviate from the expected results. Pathological concentrations of binding proteins can lead to results outside the reference range, although the patient may be in a euthyroid state. Free T3 or free T4 testing is indicated in these cases.

 

Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating antianimal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.

 

Method Description

Testing is performed on a Roche cobas instrument. The Roche triiodothyronine assay (T3) is a competitive assay using electrochemiluminescence detection. Bound T3 is released from binding proteins by 8-anilino-1-naphthalene sulfonic acid (ANS). The patient specimen is incubated with a sheep polyclonal anti-T3 antibody labeled with ruthenium. Streptavidin-coated microparticles and biotinylated T3 are added for a second incubation during which the still free binding sites of the labeled antibody become occupied. The resulting immunocomplex becomes bound to the solid phase by interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are removed and application of a voltage to the electrode induces the electrochemiluminescent emission. This signal is measured against a calibration curve to determine patient results.(Package insert: Roche cobas. Roche Diagnostics, Indianapolis, IN.)

Analytic Time

Same day/1 day

Specimen Retention Time

14 days

Clinical Information

Thyroid hormones regulate a number of developmental, metabolic, and neural activities throughout the body. The thyroid gland synthesizes 2 hormones. The 2 main hormones secreted by the thyroid gland are thyroxine, which contains 4 atoms of iodine (T4), and triiodothyronine (T3). T3 production in the thyroid gland constitutes approximately 20% of the total T3; the rest is generated by the conversion (deiodination) of T4 to T3 is also produced by conversion (deiodination) of T4 in peripheral tissues. Circulating levels of T4 are much greater than T3 levels, but T3 is biologically the most metabolically active hormone (3-4 times more potent than T4) although its effect is briefer due to its shorter half-life compared to T4.

                                                                                         

Thyroid hormones circulate primarily bound to carrier proteins (eg, thyroid-binding globulin: TBG, prealbumin, and albumin); whereas only a small fraction circulates unbound (free). Only the free forms are metabolically active. While both T3 and T4 are bound to TBG, T3 is bound less firmly than T4. Total T3 consists of both the bound and unbound fractions.

 

In hyperthyroidism, both T4 and T3 levels are usually elevated, but in a small subset of hyperthyroid patients only T3 is elevated (T3 toxicosis).

 

In hypothyroidism T4 and T3 levels are decreased. T3 levels are frequently low in sick or hospitalized euthyroid patients.

 

See Thyroid Function Ordering Algorithm in Special Instructions.

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.