Determination of thyroxine-binding globulin (TBG) levels is particularly useful in cases where total thyroid hormone levels are not correlated with thyroid metabolic status, as is often the case during pregnancy and contraceptive use.
Both thyroid hormones, triiodothyronine (T3) and thyroxine (T4) are found in the blood in two forms. Of these two forms, one is the "free" state, which allows the hormone to be biologically active while the other is the one that binds to plasma proteins. This test measures the level of thyroxine-binding globulin or thyroid-binding globulin (TBG), the major protein carrier for T3 and T4. Its measurement provides information to aid in the differential diagnosis of actual thyroid disorders from those associated with changes in TBG levels.
Possible Interpretations of Pathological Values
- Increase: Acute intermittent porphyria, active hepatitis, congenital TBG excess, estrogen-secreting tumors, HIV infection, hypothyroidism, liver disease, neonates, pregnancy, acute thyroiditis. Medications: Clofibrate, estrogen, heroin, methadone, oral contraceptives, phenothiazines
- Decrease: Acromegaly, acute disease, congenital TBG deficiency, hyperthyroidism, low albumin (liver disease), malnutrition, nephrosis, nephrotic syndrome, stress, testosterone-producing tumors. Medications: Androgens, phenytoin, prednisone, salicylates, testosterone, valproic acid
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.