Type of test Blood
Normal findings
Test explanation and related physiology TBG is the major thyroid hormone protein carrier. When it is elevated, total T3 and total T4 are also elevated. This may give the false indication that the patient has hyperthyroidism when in fact the patient just has elevated TBGs. When total T4 is elevated, one must ascertain whether that elevation is caused by an elevation in TBG or a real elevation in T4 alone, which is associated with hyperthyroidism.
The most common causes of elevated TBGs are pregnancy, hormone replacement therapy, and the use of oral contraceptives. Elevated TBGs are also present in some cases of porphyria and in infectious hepatitis. Decreased TBGs are commonly associated with other causes of hypoproteinemia (e.g., nephrotic syndrome, gastrointestinal malabsorption, and malnutrition).
Interfering factors
* Drugs that increase TBG include estrogens, methadone, oral contraceptives, and tamoxifen.
* Drugs that decrease TBG include anabolic steroids, androgens, danazol, phenytoin, propranolol, and steroids.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
• List on the laboratory slip any drugs that may affect test results.
Abnormal findings
Increased levels
- Pregnancy
- Estrogen replacement therapy
- Estrogen-producing tumors
- Infectious hepatitis
- Genetic increased TBG
- Acute intermittent porphyria
Decreased levels
- Protein-losing enteropathy
- Protein-losing nephropathy
- Malnutrition
-Testosterone-producing tumors
- Ovarian failure
- Major stress
