Serum TBG level
Key points
- Serum TBG level is a test to evaluate thyroid function by measuring the level of thyroxine binding globulin (TBG) in the blood.
- Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand.
- Several medications and conditions can interfere with TBG test results.
- When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation.
Alternative names
Serum thyroxine binding globulin; TBG level
Definition
Serum TBG level is a test to evaluate thyroid function by measuring the level of thyroxine binding globulin (TBG) in the blood. Thyroxine binding globulin is a protein that transports thyroid hormone around your body.
How the test is performed
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The area where blood is to be drawn is cleaned with antiseptic, and a tight elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Once the blood has been collected, the band is removed to restore circulation, the needle is removed, and the puncture site is covered to stop any bleeding.
The sample is then taken to the laboratory where it is evaluated by special laboratory tests, such as electrophoresis or radioimmunoassay.
How to prepare for the test
Several medications and conditions can interfere with TBG test results.
If you take any of the following, your TBG results may be elevated:
- Estrogens, found in oral contraceptives or estrogen replacement therapy
- Phenothiazines
- Heroin or methadone
If you have one of the following conditions, your TBG results may also be elevated:
- Severe liver disease
- Acute intermittent porphyria
- HIV
If you take any of the following, your TBG levels may be reduced:
- High doses of salicylates, such as aspirin
- Male hormones, such as androgens and testosterone
- Depakote or Depakene (also called valproic acid)
- Dilantin (also called phenytoin)
- Prednisone
If you have one of the following conditions, your TBG results may also be reduced:
- Nephrotic syndrome, or kidney failure
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.