Overview of Thyroxine - Free
What is Thyroxine - Free?
Preparation for Thyroxine - Free
- No special preparation required
Why Get Tested for Thyroxine - Free?
To diagnose any suspected thyroid disease (Hypothyroidism or Hyperthyroidism)
To monitor treatment in patients with thyroid diseases
Understand more about Thyroxine - Free
The thyroid gland secretes the following hormones:
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.
What Results of Thyroxine - Free mean?
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
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.
Patient Concerns about Thyroxine - Free
Frequently Asked Questions about Thyroxine - Free