TBG (Thyroxine Binding Globulin) [870X]

Test Code

CPT Codes

Preferred Specimen
1 mL serum

Minimum Volume
0.5 mL

Transport Container
Plastic screw-cap vial

Transport Temperature
Room temperature

Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days

Immunoassay (IA)

Setup Schedule
Set up: Daily evenings; Report available: Same day

Reference Range
Adult Male 12.7-25.1 mcg/mL
Adult Female 13.5-30.9 mcg/mL
  4-6 Years 14.8-32.9 mcg/mL
  7-8 Years 16.3-30.7 mcg/mL
  9-10 Years 15.8-27.4 mcg/mL
  11 Years 15.5-27.4 mcg/mL
  12 Years 14.8-26.2 mcg/mL
  13 Years 13.8-25.2 mcg/mL
  14 Years 12.2-25.2 mcg/mL
  15 Years 10.8-23.8 mcg/mL
  16 Years 10.0-23.8 mcg/mL
  17 Years 8.5-23.1 mcg/mL

Clinical Significance
Thyroxine-binding globulin (TBG), a glycoprotein produced in the liver, binds both thyroxine (T4) and triiodothyronine (T3) with high affinity. Because TBG accounts for 76% of plasma protein thyroxine-binding activity, an increase or decrease in its circulating level alters total concentrations of T4 and T3 in blood, leading to potential confusion with true thyroid gland dysfunction. A number of diseases and medications, as well as inherited alterations in TBG gene expression, can change the serum TBG concentration. Measurement of TBG is useful in distinguishing quantitative TBG derangements from thyroid dysfunction. This analyte is elevated with estrogen therapy (especially oral contraceptive agents), during pregnancy and or hepatitis. Serum TBG may be decreased in cirrhosis, in the nephritic syndrome and by androgens.

Performing Laboratory
Quest Diagnostics Nichols Institute
14225 Newbrook Drive
Chantilly, VA 20153

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.