T3 Uptake

CPT: 84479
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Test Details

Synonyms

  • Thyroid Hormone-binding Ratio (THBR)

Use

Thyroid function test for the diagnosis of hypothyroidism or hyperthyroidism, used with thyroxine (T4) or equivalent to provide free T4 index, FTI. An indirect measure of binding protein, the T3 uptake reflects available binding sites (ie, reflects TBG). T3 uptake is not a measurement of serum T3. It should never be used alone; rather, its usual application is use with thyroxine (T4).

Limitations

Alterations in binding capacity of TBG are described with major illness and with high doses of salicylates and corticosteroids; with use of heroin, methadone, phenytoin, and perphenazine. Alterations occur with malnutrition, such as in metastatic malignancy, and are found in patients with abnormal serum protein patterns (eg, nephrotic syndromes, cirrhosis). Other states in which changes in TBG occur include infancy, acromegaly, molar and ordinary pregnancy, oral contraceptives, and with exogenous hormones including androgens, anabolic steroids, and estrogens. Hereditary increase and decrease of TBG occurs.

Methodology

Cloned enzyme donor immunoassay (CEDIA)

Reference Interval

See table.1

Age

Male (%)

Female (%)

0 to 11 m

23−34

23−36

1 to 3 y

24−35

24−36

4 to 6 y

24−34

24−35

7 to 11 y

24−33

22−35

12 to 15 y

25−37

23−37

16 to 18 y

24−38

23−35

>18 y

24−39

24−39

Specimen Requirements

Specimen

Serum

Volume

1 mL (adult), 0.8 mL (pediatric)

Minimum Volume

0.5 mL (adult), 0.3 mL (pediatric) (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

Clinical Information

Special Instructions

This test reflects assessment of thyroxine-binding globulin (TBG) and should not be ordered alone.

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.

Footnotes

1. Soldin SJ, Cook J, Beatey J, et al. Pediatric reference ranges for thyroxine and tri-iodothyronine uptake. Clin Chem. 1992; 38:960.

References

Bakerman S. A, B, C's of Interpretive Laboratory Data. Greenville, NC: Interpretive Laboratory Data Inc;1984.
Burke MD. Thyroid function studies. Test strategies and interpretation of results. Postgrad Med. 1980 Dec; 68(6):169-177. 6776511
Gruhn JG, Barsano CP, Kumar Y. The development of tests of thyroid function. Arch Pathol Lab Med. 1987 Jan; 111(1):84-100. 3541847

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
001156 T3 Uptake 3050-2 001156 T3 Uptake % 3050-2

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