Description
The thyroid gland makes two thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These hormones regulate the way the body uses energy.
These hormones can be found in two forms in the blood stream: free, or attached to a protein (Thyroxine Binding Globulin). The greatest percentage of thyroid hormones are attached to TBG, while only a small part of them are free on the blood.
Thyroid hormones are important for normal development of the brain, especially during the first 3 years of life. Older children also need thyroid hormones to develop normally, and adults need the hormones to regulate the way the body uses energy (metabolism).
Its concentration is measured by means of analysis of a blood sample drawn from the vein in the arm.
Purpose of the test
To meassure the amount of Thyroxine Binding Globulin in blood in order to check the amount of thyroid hormones.
This test helps in :
• diagnose a thyroid disorder in a person with symptoms
• screen newborns for an underactive thyroid
• monitor thyroid replacement therapy in people with hypothyroidism
• diagnose and monitor female infertility problems
• help evaluate the function of the pituitary gland
• screen adults for thyroid disorders
Reference range values
mcg/mL (SI: nmol/L = 18.5 x mcg/mL)
13 - 39
Abnormal findings
If after a TSH test result high and a T4 test result normal, a T3 test result is normal, it can indicate a mild form of hypothyroidism.
If after a TSH test result high and a T4 test result low, a T3 test result is normal or low, it can indicate hypothyroidism.
If after a TSH test result low and a T4 test result normal, a T3 test result is normal, it can indicate a mild form of hyperthyroidism.
If after a TSH test result low and a T4 test result normal or high, a T3 test result is normal or high, it can indicate hyperthyroidism.
If after a TSH test result low and a T4 test result normal or low, a T3 test result is normal or low, it can indicate a nonthyroidal illness, for example a rare pituitary hypothyroidism.