Thyroxine-binding Globulin (TBG), Serum

CPT: 84442
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Expected Turnaround Time

1 - 3 days

Related Documents

For more information, please view the literature below.

Thyroid Testing: Assessing Thyroid Disease in Your Patients

Specimen Requirements




0.8 mL

Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)


Red-top tube or gel-barrier tube


If a red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions


Stability Requirements



Room temperature

7 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gross hemolysis

Test Details


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


TBG is normal in familial dysalbuminemic hyperthyroxinemia, an entity which can be incorrectly identified as thyrotoxicosis.4 Triiodothyronine uptake was described as having produced information equivalent to TBG in a study of 372 subjects.5


Immunochemiluminometric assay (ICMA)

Reference Interval

See table.1


Male (μg/mL)

Female (μg/mL)

1 to 11 m



1 to 3 y



4 to 6 y



7 to 12 y



13 to 18 y



>18 y




1. Hicks JM, Godwin ID, Beatey J, Bailey J, Bjorn S, Soldin SJ. Pediatric reference ranges for thyroid binding globulin. Clin Chem. 1993; 39:1172. Poster 248
2. Viscardi RM, Shea M, Sriwantanakul K, McCormick K. Hyperthyroxinemia in newborns due to excess thyroxine-binding globulin. N Engl J Med. 1983 Oct 13; 309(15):897-899. 6412142
3. Sarne DH, Refetoff S, Nelson JC, Linarelli LG. A new inherited abnormality of thyroxine-binding globulin (TBG-San Diego) with decreased affinity for thyroxine and tri-iodothyronine. J Clin Endocrinol Metab. 1989 Jan; 68(1):114-119. 2491856
4. Ruiz M, Rajatanavin R, Young RA, et al. Familial dysalbuminemic hyperthyroxinemia: A syndrome that can be confused with thyrotoxicosis. N Engl J Med. 1982 Mar 18; 306(11):635-639. 6173750
5. 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 Jan; 29(1):74-79.6401235


Borst GC, Eil C, Burman KD. Euthyroid hyperthyroxinemia. Ann Intern Med. 1983 Mar; 98(3):366-378 (review). 6187257
Ingbar SH. Diseases of the thyroid. In: Braunwald E, Isselbacher KJ, Petersdorf RG, et al, eds. Harrison's Principles of Internal Medicine. 11th ed. New York, NY: McGraw-Hill;1987: 1732-1752.
Nelson JC, Tomei RT. Dependence of the thyroxine/thyroxine-binding globulin (TBG) ratio and the free thyroxine index on TBG concentrations. Clin Chem. 1989 Apr; 35(4):541-544. 2495196
Oberkotter LV, Farber M. Thyroxine-binding globulin in serum and milk specimens from puerperal lactating women. Obstet Gynecol. 1984; 64(2):244-247. 6429594
Refetoff S. Inherited thyroxine-binding globulin abnormalities in man. Endocr Rev. 1989 Aug; 10(3):275-293.2506004


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
001735 Thyroxine Binding Globulin 3021-3 001735 Thyroxine Binding Globulin ug/mL 3021-3

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