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Triiodothyronine Free

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A free triiodothyronine test, most commonly referred to as a T3 test, measures the level of a hormone called triiodothyronine in your blood. T3 is a hormone secreted by the thyroid glands and is important for the metabolism of your body including the heart rate and temperature. A T3 test is required in case of symptoms like anxiety, weight loss, low tolerance for heat, and trouble sleeping. This test is most often used to diagnose hyperthyroidism, a condition in which the body makes too much thyroid hormone.

T3 test is performed with T4 and TSH tests to get a full picture of how your thyroid is functioning. Overnight fasting of 10-12 hours is advised before undergoing free triiodothyronine test.

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What does Triiodothyronine Free measure?

The Free Triiodothyronine (T3) Test measures the levels of the Free form of the T3 hormone.

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 the Pituitary gland (a gland present in the brain). It directs the thyroid gland to produce and release the thyroid hormones (T3 & T4) into your blood. The iodine absorbed from the food stimulates the thyroid glands to make the thyroid hormones.

The thyroid hormones are essential for growth and metabolism. If the thyroid gland produces very high amounts of T3 & T4 hormones, you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity towards heat, etc. and this is known as Hyperthyroidism.

The decreased production of thyroid hormones results in Hypothyroidism which may cause weight gain, fatigue, slow heart rate, increased sensitivity towards 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 the levels of thyroid hormone decrease, the pituitary gland is stimulated to release TSH. This high TSH, in turn, leads to an increase in the release of 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 the proteins present in the blood which prevents it from entering the body tissues.

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

The total T3 includes both the bound and the free forms circulating within the 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 of only 0.3% of the total T3 hormone. The two main proteins in the blood that the T3 hormone binds itself to are albumin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).

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

FAQs related to Triiodothyronine Free

What is Hyperthyroidism?

Hyperthyroidism is a condition in which the thyroid gland is overactive and there is an increased production of thyroid hormones by the thyroid gland. Causes of Hyperthyroidism include Graves’ disease, multinodular goiter, thyroid nodules, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. Diagnosis of this condition can help to relieve the symptoms and prevent long-term complications.

What are the symptoms of Hyperthyroidism?

Symptoms of Hyperthyroidism include: Rapid heartbeat (tachycardia) — commonly more than 100 beats/minute — irregular heartbeat (arrhythmia) or pounding of your heart (palpitations), sudden weight loss, nervousness, anxiety, irritability, tremor (usually a fine trembling in your hands and fingers), changes in menstrual patterns, increased sensitivity towards heat, changes in bowel patterns (especially more frequent bowel movements), an enlarged thyroid gland (goiter) which may appear as a swelling at the base of your neck, increased appetite, sweating, fatigue, muscle weakness, sleep disturbances, skin thinning, fine and brittle hair.

What is Hypothyroidism?

Hypothyroidism, also called underactive thyroid or low thyroid is a condition in which the thyroid gland does not produce enough thyroid hormones. It can be commonly caused by intake of low iodine diet or Hashimoto's thyroiditis (an autoimmune disease). Less common causes include previous treatment with radioactive iodine, injury to the pituitary gland which secretes TSH, intake of certain medicines, previous thyroid surgery, or a lack of a functioning thyroid gland at birth.

What are the symptoms of Hypothyroidism?

Hypothyroidism can cause symptoms such as tiredness (fatigue), hoarseness, constipation, feeling cold, dry skin, dry and thin hair, puffy face, weight gain, and muscle weakness. Along with that, one may experience decreased sweating, depression, slowed heart rate, increased blood cholesterol levels, pain, and stiffness in your joints, impaired memory, problems of infertility or menstrual changes, muscle stiffness, aches, and tenderness.

What additional tests your doctor may order to detect the thyroid disease?

Your doctor may order the following tests: Thyroid Stimulating Hormone (TSH) test, T3 Total Hormone test, and Thyroid Profile Test.

Is there any risk associated with this test?

There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.

How can hyperthyroidism affect a pregnant woman and her baby?

An untreated hyperthyroidism during pregnancy can lead to miscarriage, premature birth, low birth weight of the baby, preeclampsia (a very high rise in blood pressure in late pregnancy), thyroid storm (a sudden, severe worsening of symptoms of hyperthyroidism) and congestive heart failure.

How can hypothyroidism affect a pregnant woman and her baby?

An untreated hypothyroidism during pregnancy can cause preeclampsia (a very high rise in blood pressure in late pregnancy), anemia, miscarriage, low birth weight of the baby, stillbirth (death or loss of a baby before or during delivery) and rarely, congestive heart failure. These problems are noticed mostly as a result of severe hypothyroidism. The mother’s thyroid hormones play an important role in the development of the baby’s brain and nervous system. Untreated hypothyroidism, especially during the first trimester can cause low IQ and can hinder the baby’s normal development.

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