What is Total T4 (TT4)?
T4 (Thyroxine) is a thyroid hormone that is produced by the thyroid gland and plays an important role in the body’s metabolism. Nearly all the T4 (and T3) found in the blood is bound to protein. The rest is free (unbound) and is the biologically active form of the hormone. A total T4 test measures the total amount of T4 in the blood.
Why test TT4 (total T4)?
Health check
Discover your risk factors for lifestyle diseases in time to do something about them.
Full thyroid panel
TT4 is an important part of a complete thyroid panel.
Symptoms
Symptoms of thyroid disorder include depression, weakness, fatigue, sleeping problems, sensitivity to heat/cold, dry skin, hair loss, increased heart rate, and infertility.
Monitoring
Monitor an existing thyroid condition as you make dietary and lifestyle changes or take medication. We can send any results to your doctor.
What do the results mean?
What causes low total T4?
Low Total T4 indicates that the thyroid does not produce enough thyroid hormone (hypothyroidism). Low T4 may indicate iodine deficiency.
What causes high total T4?
High Total T4 suggests an excess production of thyroid hormone (hyperthyroidism).
More information
Thyroid hormones play an important role in the body's metabolism. T4 (thyroxine) is an important hormone that is produced by the thyroid gland and transported by the blood to the body's cells. T4 can be either free (unbound) or bound to protein in your blood. Nowadays, most health providers consider free T4 to be the most important test. However, measuring total T4 and other thyroid markers provides a more complete picture.
If the thyroid gland produces too much hormone, symptoms are those of a raised metabolism, including rapid heart rate, sweating, increased appetite, weight loss, tremors, and poor sleep. Low thyroid hormone has the opposite effect, with side effects such as feeling cold, fatigue, weight gain, hair loss, and constipation, and the other signs and symptoms noted above.
TSH stimulates the production and release of T4 (primarily) and T3 from the thyroid gland. Thyroid health is somewhat complex and your practitioner should take into account the following:
Blood test results: Free T4, free T3, TSH. Do you produce enough thyroid hormone? Is your T4 converting properly to T3? Is your TSH within an optimal range?
Symptoms: If the above is within the normal range, but you have symptoms or are pregnant, thyroid antibody testing should be undertaken.
Individual differences and your results: Do you have symptoms and your results are low or high normal? Perhaps these levels are too low or high for you.
Instructions
No advance preparation is needed for this test.
On the day of the test
Do not take your thyroid medication until after you have taken this test. Remember to take I.D. with you when going to take a test. Do not work out before going to do this test, as this may affect your results.
Take this test before 10 am, as results can vary throughout the day. If you are repeating a test, try to take it at the same time of day.