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- Thyroid Hormone-binding Ratio (THBR)
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.
Expected 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.
Related Information
Related Documents
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
If a red-top tube or plasma is used, transfer separated serum or plasma 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 |
Test Details
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
Electrochemiluminescence Immunoassay (ECLIA)
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 |
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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