Second-order testing for hyperthyroidism in patients with low thyroid-stimulating hormone values and normal thyroxine levels
Diagnosis of triiodothyronine toxicosis
This test is not useful for general screening of the population without a clinical suspicion of hyperthyroidism.
See Thyroid Function Ordering Algorithm in Special Instructions.
Electrochemiluminescence Immunoassay
T3 Suppression
T3 Total, Serum
Total T3, Serum
Triiodothyronine (T3)
Triiodothyronine, Total T3
Thyroid Function Cascade
T3 (Triiodothyronine), Total Only, Serum
Triiodothyronine
See Thyroid Function Ordering Algorithm in Special Instructions.
Serum
Patient Preparation: For 12 hours before specimen collection do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
0.75 mL
Gross hemolysis | Reject |
Gross lipemia | OK |
Gross icterus | OK |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Refrigerated (preferred) | 7 days | |
Frozen | 30 days |
Second-order testing for hyperthyroidism in patients with low thyroid-stimulating hormone values and normal thyroxine levels
Diagnosis of triiodothyronine toxicosis
This test is not useful for general screening of the population without a clinical suspicion of hyperthyroidism.
See Thyroid Function Ordering Algorithm in Special Instructions.
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.
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 (> or =20 years): 80-200 ng/dL
For SI unit Reference Values, see www.mayocliniclabs.com/order-tests/si-unit-conversion.html
Triiodothyronine (T3) values above 200 ng/dL in adults or over 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.
Triiodothyronine (T3) is not a reliable marker for hypothyroidism.
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 anti-animal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.
T3 has a 15-fold higher affinity for thyroid receptor compared to T4.
1. Hay ID, Klee GG: Linking medical needs and performance goals: clinical and laboratory perspectives on thyroid disease. Clin Chem. 1993;39:1519-1524
2. Klee GG: Clinical usage recommendations and analytic performance goals for total and free triiodothyronine measurements. Clin Chem. 1996;42:155-159
3. Freedman DB, Halsall D, Marshall WJ, Ellervik C: Thyroid disorders. In: Rifai N, Horvath AR, Wittwer CT: eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:1572-1616
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; 08/2019)
Monday through Friday
This test has been cleared, approved, or is exempt by the US 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.
84480
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
T3 | T3 (Triiodothyronine), Total, S | 83124-8 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
T3 | T3 (Triiodothyronine), Total, S | 83124-8 |