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TBG (Thyroxine Binding Globulin)
Test Code807
CPT Codes
84442
Preferred Specimen
1 mL serum
Minimum Volume
0.5 mL
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days
Refrigerated: 7 days
Frozen: 28 days
Methodology
Immunoassay (IA)
Setup Schedule
A.M. Sets up 1 day a week.
Report Available
Reports in 2 days.
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.
