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Triiodothyronine Total
Overview
What is T3?
The Triiodothyronine (T3) Total test is used to measure Triiodothyronine (T3) hormone in the blood. T3 hormone is secreted by the thyroid gland. It is essential for growth and metabolism.
The test is performed to help evaluate thyroid gland function, diagnose thyroid disease, including hyperthyroidism and hypothyroidism. It also helps monitor treatment efficacy in patients with thyroid disease.
A high T3 level may indicate hyperthyroidism, symptoms like weight loss, rapid heartbeat, tremors, anxiety, and increased sensitivity to heat. A decreased production of T3 hormone may be indicative of hypothyroidism which may cause symptoms like weight gain, fatigue, increased sensitivity to cold, and slow heart rate.
The T3 levels can be managed by taking medication and possibly making a few dietary and lifestyle changes.
Why is T3 done?
To diagnose thyroid diseases (Hypothyroidism or Hyperthyroidism)
To monitor treatment in patients with thyroid diseases
What does T3 Measure?
Triiodothyronine (T3) Total Test measures the total levels (both free and bound forms) of Triiodothyronine (T3) hormone in the blood.
The thyroid gland secretes the following hormones:
Triiodothyronine (T3)
Thyroxine (T4)
Thyroid Stimulating Hormone (TSH) is a hormone secreted into the blood by a gland present in the brain (Pituitary gland) and it tells your thyroid gland to make and release the thyroid hormones (T3 & T4) into your blood. The thyroid gland uses iodine from food to make the thyroid hormones.
The thyroid hormones are essential for growth and metabolism. If the thyroid gland produces very high amounts of these hormones (T3 and T4), you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity to heat etc. and this is known as Hyperthyroidism.
Also, the decreased production of thyroid hormones (T3 and T4) results in Hypothyroidism which may cause symptoms like weight gain, fatigue, slow heart rate, increased sensitivity to cold, depression, dry and thin hair etc.
There is a feedback system in the body to maintain stable amounts of the thyroid hormones (T3 and T4) in the blood. When thyroid hormone levels decrease, the pituitary gland is stimulated to release TSH. This high TSH in turn leads to the release of more thyroid hormones (T3 & T4) from the thyroid gland and vice-versa.
Majority of the T3 hormone is formed from T4 hormone and a smaller fraction is produced directly by the thyroid gland. T3 hormone circulates in the blood in two forms:
1) Bound form - It is bound to proteins present in blood and this prevents it from entering body tissues. The two main proteins in the blood that the T3 hormone is bound to are albumin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).
2) Free form - It enters the body tissues where it is needed and this is the active form. Free Triiodothyronine (FT3) constitutes only 0.3% of the total T3 hormone.
The total T3 includes both bound and free forms circulating in the blood and can be affected by the amount of protein available in the blood to bind to them. The T3 hormone can be measured as Free T3 or Total T3. Triiodothyronine (T3) Total Test measures the total levels (both free and bound forms) of Triiodothyronine (T3) hormone in the blood and is usually done as a part of the Thyroid Profile Total test which includes two more tests: Thyroid Stimulating Hormone (TSH) and Thyroxine Total (T4) hormone.
Interpreting T3 results
Interpretations
T3 (Triiodothyronine), Total Reference Range(s)
<1 Month | Not established | ||
1-23 Months | 117-239 ng/dL | ||
2-12 Years | 105-207 ng/dL | ||
13-20 Years | 86-192 ng/dL | ||
>20 Years | 76-181 ng/dL |
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about T3
Frequently Asked Questions about Triiodothyronine Total

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