Compare this test’s laboratory options
TBG (Thyroxine Binding Globulin)
Quest Diagnostics1 test optionFrom $38.03
TBG (Thyroxine Binding Globulin)
Quest DiagnosticsCatalog information reviewed: August 24, 2026 by the Sunridge Medical clinical team.
What this laboratory test evaluates
DetailsTBG (Thyroxine Binding Globulin) – 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.
What type of sample is required for this test?1 mL serum
Test ResourcesFor more information, please consult your healthcare provider.
Additional test information
TBG (Thyroxine Binding Globulin) – 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.
Collection and processing
- Sample type: Serum
- Fasting: No
- Estimated laboratory processing: Results should be available in 2 – 5 business days after the sample is collected
How Sunridge uses laboratory information
Sunridge considers the medical question, symptoms, history, medications, prior results, and whether the finding could change care before recommending testing. A laboratory result is not interpreted in isolation and does not establish a diagnosis by itself.
Before requesting this test
Availability, collection requirements, eligibility, and processing estimates can change. Sunridge reviews each request and, when appropriate, creates the order through Fullscript. Follow the current instructions supplied with the approved order.
Common questions about this laboratory test
- What sample does this test require?
- The listed sample type is Serum. Confirm current collection instructions in the approved order.
- Does this test require fasting?
- The current catalog record lists fasting as: No. Follow the instructions supplied with the approved order.
- How long does laboratory processing usually take?
- Results should be available in 2 – 5 business days after the sample is collected. Timing can change after collection or if a laboratory requires additional review.
About this test
DetailsTBG (Thyroxine Binding Globulin) - 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.
What type of sample is required for this test?1 mL serum
Test ResourcesFor more information, please consult your healthcare provider.
Additional details
TBG (Thyroxine Binding Globulin) - 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.
Highlighted health areas
- Hormones
- Thyroid
Biomarkers and report focus
The exact analytes and report format can change. Confirm the current contents in the Fullscript order before payment.
- TBG (Thyroxine Binding Globulin)