Thyroxine T4 – Total
The thyroid gland produces the main hormone thyroxine, also known as T4, which is then converted into T3 (triiodothyronine). The pituitary gland produces another hormone)TSH (thyroid stimulating hormone) that controls the production of T4. If the amount of T4 is less, then pituitary produces more TSH to stimulate the production of T4. If the levels of T4 go above a certain range, then the production of TSH is stopped by the pituitary gland. In this way, the pituitary gland helps in maintaining appropriate levels of the thyroid hormone in the body.
The majority of the T4 is bound to proteins called thyroxine binding globulin and about 0.05% or less than 1% circulates freely. A Total Thyroxine T4 Test measures both the bound and free thyroxine.
Why is the test ordered?
The test may be ordered to detect thyroid disorders, evaluate thyroid gland function and also to monitor treatment. Total Thyroxine T4 Test is a good indicator of the thyroid function when the thyroid binding proteins are normal and also when a non-thyroidal disease is absent.
When is the test ordered?
A Total T4 Test may be advised by a physician to determine the cause when the TSH test results indicate abnormalities. Typical signs and symptoms associated with thyroid disorder include
- Changes in weight
- Issues with the eyes
- Dry skin
- Hair loss
- Irregular heartbeat
- Increased heart rate
- Sensitivity to light.
How is the sample collected?
A blood sample is collected from a vein in the arm.
How to prepare for the test?
It is better to inform the doctor about all the medicines that the patient is on, before taking the test.