What is Total T3 (TT3)?
T3 (triiodothyronine) is a thyroid hormone produced directly by the thyroid and by the conversion of another thyroid hormone known as T4 (thyroxin). Together, T3 and T4 regulate your body temperature, metabolism, and heart rate.
Most of your T3 is attached to proteins. The part that is bound to proteins is known as Total T3 (TT3). This is the part that is tested here. T3, both total and free, is measured to detect a problem with your thyroid hormones.
Why test TT3?
Unless this is ordered as a retest or for a specific reason, we recommend ordering this as part of a health test.
Health check
Discover your risk factors for lifestyle diseases in time to do something about them.
Full thyroid panel
TT3 is an important marker included in a complete Thyroid Panel.
Symptoms
Thyroid disorder can present symptoms such as weakness, fatigue, sleeping problems, increased sensitivity to heat or cold, weight loss or gain, dry or puffy skin, hair loss, increased heart rate, or constipation.
Monitoring
To monitor an existing thyroid condition as you make changes to your diet or take medication. You can send your results to your doctor.
What do the results mean?
Thyroid tests cannot be interpreted individually. They must be interpreted considering your other thyroid test results and preferably medical history. A normal T3 suggests that you are producing enough T4 and converting it adequately to T3. However, this alone does not rule out thyroid problems. If you still have symptoms and your TSH, free T4, and free T3 are normal, we recommend testing your thyroid antibodies.
What causes low total T3 levels?
Low total T3 means that you have less T3 than expected. This may be because the thyroid is having trouble producing T3 and/or converting the primary thyroid hormone T4 (thyroxine) into T3. Lower levels of thyroid hormones tend to indicate an underactive gland (hypothyroidism). This test result alone is not diagnostic but will be considered alongside the results of other thyroid hormones and antibodies.
Calorie restriction can significantly lower thyroid hormones, as can stress, low carbohydrate diets, low estrogen, insulin resistance, chronic pain, low testosterone, low growth hormone, and alcohol. Nutrient deficiencies that can affect the conversion of T4 to T3, resulting in lower T3 include iodine, selenium, zinc, iron, chromium, copper, vitamin A, and B vitamins. Some supplements can lower thyroid hormones.
Note that reference ranges may be different during pregnancy.
What Causes high total T3 levels?
A high total T3 level suggests an overproduction of thyroid hormone (hyperthyroidism). It may also be associated with iodine deficiency.
More information
Thyroid problems include hyperthyroidism (overproduction of thyroid hormones), hypothyroidism (underproduction of thyroid hormones), Hashimoto’s Thyroiditis, and Graves Disease (two autoimmune thyroid conditions).
Instructions
No preparation is needed prior to this test.
On the day of the test
Do not take your thyroid medication until after you have taken this test. Always take your 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.
Arrive early and sit down quietly for 15 minutes before the test is taken.