Test Details
Methodology
Electrochemiluminescence Immunoassay (ECLIA)
Result Turnaround Time
Within 1 day
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
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).
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.
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.
Specimen Requirements
Specimen
Serum (preferred) or plasma
Volume
1 mL (adult), 0.8 mL (pediatric)
Minimum Volume
0.7 mL (adult), 0.3 mL (pediatric) (Note: This volume does not allow for repeat testing.)
Container
Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.
Collection Instructions
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Stability Requirements
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 |
Storage Instructions
Room temperature
References
Footnotes
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 |
| Order Code | 001156 | |||||
| Order Code Name | T3 Uptake | |||||
| Order Loinc | 3050-2 | |||||
| Result Code | 001156 | |||||
| Result Code Name | T3 Uptake | |||||
| UofM | % | |||||
| Result LOINC | 3050-2 |