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TBG blood test
The TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine-binding globulin (TBG).
Normal Results
Normal range is 13 to 39 micrograms per deciliter (mcg/dL), or 0.13 to 0.39 milligrams per liter (mg/L).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
An increased TBG level may be due to:
- Acute intermittent porphyria (a rare metabolic disorder)
- Hypothyroidism (underactive thyroid)
- Liver disease, such as hepatitis
- Pregnancy (TBG levels normally increased during pregnancy)
Note: TBG levels are normally high in newborns.
Decreased TBG levels may be due to:
- Acute illness
- Acromegaly (disorder caused by too much growth hormone)
- Hyperthyroidism (overactive thyroid)
- Malnutrition
- Nephrotic syndrome (symptoms that show kidney damage is present)
- Stress from surgery
High or low TBG levels affect the relationship between total T4 and free T4 blood tests. A change in TBG blood levels can alter the appropriate dose of levothyroxine replacement for persons with hypothyroidism.
Alternative Names
Serum thyroxine binding globulin, TBG level, Serum TBG level, Hypothyroidism - TBG, Hyperthyroidism - TBG, Underactive thyroid - TBG, Overactive thyroid - TBG thyroid hormone binding globulin
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