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Triiodothyronine (T3)

CPT: 84480
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Synonyms

  • T3, Total

Special Instructions

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.


Expected Turnaround Time

Within 1 day



Related Documents

For more information, please view the literature below.

Thyroid Testing: Assessing Thyroid Disease in Your Patients


Specimen Requirements


Specimen

Serum


Volume

0.8 mL


Minimum Volume

0.3 mL (Note: This volume does not allow for repeat testing.)


Container

Red-top tube or gel-barrier tube


Collection

If a red-top tube is used, transfer separated serum to a plastic transport tube.


Storage Instructions

Room temperature


Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3


Causes for Rejection

Citrate plasma specimen; improper labeling


Test Details


Use

Thyroid function which is particularly useful in the diagnosis of T3 thyrotoxicosis, in which T3 is increased and T4 is within normal limits. T3 toxicosis is occasionally found in Graves' disease. It occurs with a single toxic nodule, multinodular thyrotoxicosis, and following treatment with T3 (Cytomel®).2 It is increased in and occasionally helpful for confirmation of diagnosis of conventional hyperthyroidism, in which commonly both T3 and T4 levels are increased. T3 is needed in patients with clinical evidence for hyperthyroidism, in whom the usual thyroid profile is normal or borderline.

Reported to be normal to slightly increased with familial dysalbuminemic hyperthyroxinemia.

Recommended for patients with supraventricular tachycardia, for patients with fatigue and weight loss not otherwise explained, or for those with proximal myopathy and in whom T4 levels are not elevated.3


Limitations

T3 is decreased with nonthyroidal chronic diseases and influenced by the state of nutrition. It is not helpful for evaluation of hypothyroidism. It may be normal with thyrotoxicosis (thyroxine thyrotoxicosis).4

Variations in TBG and other binding proteins can affect T3. Such increases may be found with use of oral contraceptives, pregnancy, and other binding protein abnormalities. Fasting causes T3 and TSH to decrease.5


Methodology

Electrochemiluminescence immunoassay (ECLIA)


Reference Interval

See table.1

Age

Range (ng/dL)

0 to 3 d

96−292

4 to 30 d

62−243

31 d to 12 m

81−281

13 m to 5 y

83−252

6 to 10 y

92−219

>10 y

71−180


Additional Information

Increased T3 often occurs in hyperthyroidism, but in approximately 5% of cases only T3 is elevated, “T3 toxicosis.” Do not confuse T3 with T3 uptake; these are two different tests. The latter is done very commonly as part of the usual thyroid profile. Less than 1% of T3 is unbound.


Footnotes

1. Reference Intervals for Children and Adults.Elecsys Thyroid Test. Roche Diagnostics; May 2005.
2. Bethune JE. Interpretation of thyroid function tests. Dis Mon. 1989 Aug; 35(8):541-595. 2670494
3. Morley JE, Slag MF, Elson MK, Shafer RB. The interpretation of thyroid function tests in hospitalized patients. JAMA. 1983 May 6, 249(17):2377-2379. 6403725
4. Blank MS, Tucci JR. A case of thyroxine thyrotoxicosis. Arch Intern Med. 1987 May; 147(5):863-864. 3579439
5. Unger J. Fasting induces a decrease in serum thyroglobulin in normal subjects. J Clin Endocrinol Metab. 1988 Dec; 67(6):1309-1311. 3192683

References

Greenspan FS, Rapoport B. Thyroid gland. In: Greenspan FS, Forsham PH, eds. Basic and Clinical Endocrinology. Los Altos, Calif: Lange Medical Publications;1983:153.
Ingbar SH. Diseases of the thyroid. In: Braunwald E, Isselbacher KJ, Petersdorf RG, et al, eds. Harrison's Principles of Internal Medicine. 11th ed. New York, NY: McGraw-Hill; 1987:1732-1752.
Takamatsu J, Kuma K, Mozai T. Serum tri-iodothyronine to thyroxine ratio: A newly recognized predictor of the outcome of hyperthyroidism due to Graves' disease. J Clin Endocrinol Metab. 1986 May; 62(5):980-983. 3754263
Watts NB, Keffer JH. Practical Endocrine Diagnosis. 4th ed. Philadelphia, Pa: Lea & Febiger;1989.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
002188 Triiodothyronine (T3) 3053-6 002188 Triiodothyronine (T3) ng/dL 3053-6

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