Serum TBG level
Alternative names:
serum thyroxine binding globulin; TBG level
How the test is performed:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, 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 electrophoresis or radioimmunoassay.
How to prepare for the test:
Several medications can interfere with TBG test results. If you take any of the following, your TBG results may be elevated: If you take any of the following, your TBG levels may be depressed: - high doses of salicylates (such as aspirin)
- androgens
- Dilantin
- prednisone
If you take any of these medications, inform your health care provider before the test, since you may need to withhold your medication.
If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.
How the test will feel:
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed:
Your health care provider may use this test to identify abnormalities with your thyroid binding globulin, or to assist in diagnosing other thyroid disorders such as hypothyroidism.
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