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.

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
• Other conditions that cause low albumin levels, such as liver disease

If you take any of these medications, or have any of these conditions, inform your doctor before the test, since you may need to withhold your medication, or have another test.

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 him/her, and the purpose for the procedure, the less anxiety he/she will feel.

• Pregnancy (TBG levels are normally elevated during pregnancy)
• Hypothyroidism
• Liver disease
• Acute intermittent porphyria
• TBG levels are normally elevated in newborns

• Hyperthyroidism
• Acromegaly
• Stress from surgery
• Acute illness
• Malnutrition (from the low levels of blood protein)
• Nephrotic syndrome

• Excessive bleeding.
• Fainting or feeling lightheaded.
• Hematoma, or blood accumulating under the skin.
• Infection (a slight risk any time the skin is broken).
• The person taking the blood may have to make multiple punctures to locate veins.