Thyroid related
Thyroid binding globulin (TBG)

Author: Nat Pernick, M.D. (see Authors page)

Revised: 23 February 2016, last major update March 2011

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Thyroid binding globulin [title]
Cite this page: Thyroid binding globulin (TBG). website. Accessed October 25th, 2016.
Definition / General
  • Deficiency does not cause thyroid disease by itself
  • Increases / decreases cause increase / decrease in total T3 and T4
  • However, free T3 and T4 are unchanged
  • Produced in liver
  • Major carrier protein for T3 and T4
  • Has highest affinity, but lowest concentration of the carrier proteins
  • Other thyroid carrier proteins are transthyretin and albumin, which have lower affinity but higher concentration
  • Interpreting T3 and T4 levels that do not match clinical findings or other laboratory results
    • For example, total T3 and T4 levels are very low, TSH is normal, free T3 and T4 are normal, patient is clinically euthyroid

  • Chemiluminescence immunoassay

Reference range
  • 13 - 39 μg/dL (150 - 360 nmol/L)

High values
  • Inherited abnormalities, drugs (clofibrate, estrogens, 5-FU, heroin/methadone), hepatitis, pregnancy, idiopathic)

Low values
  • Inherited abnormalities, drugs (androgens, glucocorticoids), liver failure, malnutrition, nephrotic syndrome, idiopathic)
Additional References