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Thyroxine - Free

360
4.7
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Overview
Interpreting Results
FAQ's

Overview of FT4

What is FT4?

Thyroxine (T4) is a hormone secreted by the thyroid gland (small, butterfly-shaped gland located in front of the neck). The T4 hormone is essential for growth and metabolism. T4 circulates in the blood in two forms: Free form (FT4) and Bound form. Free Thyroxine (T4) test measures the free form of Thyroxine hormone in the blood.

Why is FT4 done?

  • To diagnose any suspected thyroid disease (Hypothyroidism or Hyperthyroidism)

  • To monitor treatment in patients with thyroid diseases




What does FT4 Measure?

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.

T4 hormone constitutes about 90% of thyroid hormones and 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 three main proteins in the blood that the T4 hormone is bound to are albumin, transthyretin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).

 

2) Free form - It enters the body tissues where it's needed and this is the active form. Free Thyroxine (FT4) constitutes only 0.3% of the total T3 hormone.

 

Hence, the T4 hormone can be measured as Free T4 or Total T4. The total T4 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. Therefore, Thyroxine (T4) Free test is a useful indicator of T4 levels in the blood when binding proteins are increased or decreased.

 

Thyroxine (T4) Free test is also done as a part of the Thyroid Profile Free test which includes two more tests: Thyroid Stimulating Hormone (TSH) and Triiodothyronine (T3) Total.

Preparation for FT4

  • No special preparation required

Sample Type for FT4

The sample type collected for Thyroxine - Free is: Blood

Interpreting FT4 results

Interpretations


Age

FT4 (pmol/L)

Newborn

11.0 - 32.0

6 days to 3 months

11.5 - 28.3

4 to 12 months

11.9 - 25.6

1 to 6 years

12.3 - 22.8

7 to 11 years

12.5 - 21.5

12 to 20 years

12.6 - 21.0

Adults

12.0 - 22.0


High values than normal reference range are seen in hyperthyroidism and patients with acute thyroiditis.

Low values than normal reference range are seen in hypothyroidism, myxedema, cretinism, chronic thyroiditis, and occasionally, subacute thyroiditis.



Answers to Patient Concerns & Frequently Asked Questions (FAQs) about FT4

Frequently Asked Questions about Thyroxine - Free

Q. What is Hyperthyroidism?
Hyperthyroidism is a condition in which the thyroid gland is overactive. This leads to 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, overconsumption of iodine, and excess of synthetic thyroid hormone. Diagnosis of this condition can help relieve the symptoms and prevent long-term complications.
Q. 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.
Q. 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 low intake of iodine in diet or Hashimoto's thyroiditis (an autoimmune disease). Other 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 improper functioning of thyroid gland since birth.
Q. What are the symptoms of Hypothyroidism?
Symptoms of Hypothyroidism include: Tiredness (fatigue), constipation, feeling cold, dry skin, weight gain, muscle weakness, decreased sweating, depression, slower 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, hoarseness, puffy face, dry and thin hair.
Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood sample from a blood vessel in your arm generally from the inner side of the elbow area. The doctor, nurse or the phlebotomist will tie an elastic band around your arm which will help the blood vessels to swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You may feel a tiny pinprick during the procedure. Blood sample once collected is then sent to the laboratory.
Q. 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.
Q. 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.
Q. 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 birthweight, 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 baby’s brain and nervous system, untreated hypothyroidism, especially during the first trimester can cause low IQ and other problems with normal development.
Q. Is there any preparation required before the test?
Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.
Q. 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.
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Thyrocare Technologies Limited is India's first and most advanced Totally Automated Laboratory having its strong presence in more than 2000 cities / towns in India and internationally. Thyrocare is India's first fully automated diagnostic laboratory with a focus on providing quality at affordable costs to laboratories and hospitals in India and other countries. Thyrocare operates with a Centralized Processing Laboratory (CPL) in Mumbai - India for esoteric tests; and Regional Processing Laboratory in major metro cities of India and other parts of Asia. We have focus on strong technologies, strong brands and strong systems that enable all laboratories to give their clients the best of science and technology at an affordable cost. With a belief that 'Quality' is the heart of any intelligent management, Thyrocare became one of the first Indian diagnostic laboratories to obtain internationally renowned quality accreditations like ISO 9001-2000 rating as early as 2001, which is now escalated to ISO 9001:2008; NABL (National Accreditation Board for Testing and Calibration Laboratories) in 2005 and CAP (College of American Pathologists) certification in 2007.
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