Thyroxine-Binding Globulin (TBG), Serum
| Thyroxine-Binding Globulin (TBG), Serum | | | |
| Number | | 001735 |
| CPT | | 84442 |
| Related Information | | Thyroxine (T4) Free, Direct, Serum Tri-iodothyronine (T3) |
| Synonyms | | TBG |
| Specimen | | Serum |
| Volume | | 0.5 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 | | Refrigerate |
| Reference Interval | | See table.1
| Age | Male
(μg/mL) | Female
(μg/mL) | | 1-11 mo | 16-33 | 18-32 | | 1-3 y | 16-32 | 19-34 | | 4-6 y | 17-30 | 18-31 | | 7-12 y | 17-29 | 15-29 | | 13-18 y | 13-26 | 14-29 | | >18 y | 13-39 | 13-39 |
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| Use | | Distinguish between high T4 levels due to hyperthyroidism and due to increased binding by TBG in euthyroid individuals who have normal levels of free hormones; document cases of hereditary deficiency or increase of TBG; work-up of thyroid disease. In patients with low T4, high T3 (uptake) or the reverse, who clinically seem eumetabolic and have normal FTI, measurement of TBG is only occasionally needed. Some such patients may have hereditary anomalies of TBG. TBG is increased by estrogens, tamoxifen, pregnancy, perphenazine, and in some cases of liver disease, including hepatitis. Decreased TBG is found with some instances of chronic liver disease, nephrosis and systemic disease and with large amounts of glucocorticoids, androgens/anabolic steroids, and acromegaly. Although alterations of TBG are usually resolved by the thyroid profile, TBG must occasionally be directly measured. Kindreds are described with elevated TBG and hyperthyroxinemia as a harmless genetic abnormality. They have normal levels of TSH and free T4 and decreased T3 uptake.2 Structural variants of TBG are inherited as X-chromosome linked traits, most inherited structural abnormalities in TBG cause decreased affinity for thyroid hormone.3 |
| Limitations | | TBG is normal in familial dysalbuminemic hyperthyroxinemia, an entity which can be incorrectly identified as thyrotoxicosis.4 Tri-iodothyronine uptake was described as having produced information equivalent to TBG in a study of 372 subjects.5 |
| Methodology | | Immunochemiluminometric assay (ICMA) |
| Footnotes | | - Hicks JM, Godwin ID, Beatey J, et al, “Pediatric Reference Ranges for Thyroid Binding Globulin,” Clin Chem, 1993, 39:1172.
- Viscardi RM, Shea M, Sriwantanakul K, et al, “Hyperthyroxinemia in Newborns Due to Excess Thyroxine-Binding Globulin,” N Engl J Med, 1983, 309(15):897-9.
- Sarne DH, Refetoff S, Nelson JC, et al, “A New Inherited Abnormality of Thyroxine-Binding Globulin (TBG-San Diego) With Decreased Affinity for Thyroxine and Tri-iodothyronine,” J Clin Endocrinol Metab, 1989, 68(1):114-9.
- Ruiz M, Rajatanavin R, Young RA, et al, “Familial Dysalbuminemic Hyperthyroxinemia: A Syndrome That Can Be Confused With Thyrotoxicosis,” N Engl J Med, 1982, 306(11):635-9.
- Wilke TJ, “Free Thyroid Hormone Index, Thyroid Hormone/Thyroxine-Binding Globulin Ratio, Tri-iodothyronine Uptake, and Thyroxine-Binding Globulin Compared for Diagnostic Value Regarding Thyroid Function,” Clin Chem, 1983, 29(1):74-9
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| References | | Borst GC, Eil C, and Burman KD, “Euthyroid Hyperthyroxinemia,” Ann Intern Med, 1983, 98(3):366-78 (review). Ingbar SH, “Diseases of the Thyroid,” Harrison's Principles of Internal Medicine, 11th ed, Braunwald E, Isselbacher KJ, Petersdorf RG, et al, eds, New York, NY: McGraw-Hill, 1987, 1732-52. Nelson JC and Tomei RT, “Dependence of the Thyroxine/Thyroxine-Binding Globulin (TBG) Ratio and the Free Thyroxine Index on TBG Concentrations,” Clin Chem, 1989, 35(4):541-4. Oberkotter LV and Farber M, “Thyroxine-Binding Globulin in Serum and Milk Specimens From Puerperal Lactating Women,” Obstet Gynecol, 1984, 64(2):244-7. Refetoff S, “Inherited Thyroxine-Binding Globulin Abnormalities in Man,” Endocr Rev, 1989, 10(3):275-93. |
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