T3 Uptake

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Category:

Turnaround Time: Within 1 day
CPT Code:

84479

Test Type: 1 mL (adult), 0.8 mL (pediatric) Serum
Stability Time:

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3
Reference Range:

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

Overview:

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).

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.

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

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. PubMed 6776511

Gruhn JG, Barsano CP, Kumar Y. The development of tests of thyroid function. Arch Pathol Lab Med. 1987 Jan; 111(1):84-100. PubMed 3541847

Collection Details:

Collection Instructions:

Red-top tube or gel-barrier tube.

If a tube other than a gel-barrier tube is used, transfer separated serum to a plastic transport tube.

Room temperature