TriIodothyronine Free

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 release of more thyroid hormones (T3 & T4) from the thyroid gland and vice-versa.

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.

2) Free form - It enters the body tissues where it's needed and thus is the active form.

The total T3 includes both bound and free forms circulating in blood and can be affected by the amount of protein available in the blood to bind to them.

Majority of the T3 hormone is formed from T4 hormone and a smaller fraction is produced directly by the thyroid gland. Free Triiodothyronine (FT3) constitutes only 0.3% of the total T3 hormone. The two main proteins in blood that the T3 hormone is bound to are albumin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).

Hence, T3 hormone can be measured as Free T3 or Total T3. Free Triiodothyronine (T3) Test is also done as a part of Thyroid profile Free test which includes two more tests : Thyroid Stimulating Hormone (TSH) and Free Thyroxine (FT4).

The thyroid gland secretes the following hormones:

• Triiodothyronine (T3)

• Thyroxine (T4)

• Calcitonin

Thyroid Stimulating Hormone (TSH), also called Thyrotropin 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 release of more thyroid hormones (T3 & T4) from the thyroid gland and vice-versa.

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.

2) Free form - It enters the body tissues where it's needed and thus is the active form.

The total T3 includes both bound and free forms circulating in blood and can be affected by the amount of protein available in the blood to bind to them.

Majority of the T3 hormone is formed from T4 hormone and a smaller fraction is produced directly by the thyroid gland. Free Triiodothyronine (FT3) constitutes only 0.3% of the total T3 hormone. The two main proteins in blood that the T3 hormone is bound to are albumin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).

Hence, T3 hormone can be measured as Free T3 or Total T3. Free Triiodothyronine (T3) Test is also done as a part of Thyroid profile Free test which includes two more tests : Thyroid Stimulating Hormone (TSH) and Free Thyroxine (FT4).