The thyroid hormone thyroxine (T4) is a kind of thyroid hormone. Thyroid disorders can be determined using a thyroxine test. The thyroid gland is a tiny, butterfly-shaped gland that is located near the throat. The thyroid produces hormones that control the way your body uses energy. It also helps you maintain a healthy weight, body temperature, physical strength, and even mood. This test is used to determine how much T4 is in the blood. Thyroid illness might be indicated by elevated levels of Thyroxine or decreased levels of the same. T4 (thyroxine) is the most significant hormone produced by the thyroid gland.
The nomenclature T4 comes from the fact that the thyroxine molecule is composed of four iodine atoms.
Thyroid hormones are necessary for brain development in children and many important physiological processes in adults. T4 is commonly seen in abundant amounts in the bloodstream. The majority of the circulating T4 is bound to proteins and is not readily available for utilization by the body, the other is free T4 which is readily available and used by the cells also known as bioavailable T4.
There are two types of T4 hormone:
- One is free T4 or also known as unbound T4 or bioavailable T4 which can enter the body tissues where it is required.
- The second is Bound T4 which is bound to proteins and prevents them from accessing bodily tissues. More than 99% of total T4 is bound.
A total T4 test measures both bioavailable/free and bound T4. Whereas free T4 assays only concentrate on free T4. For evaluating thyroid function, free/bioavailable T4 testing is considered more accurate than a total T4 test.
Thyroxine level test can be employed for the following:
It can also be utilised when an individual exhibits symptoms that could indicate a thyroid problem. Hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) are both common thyroid disorders. A healthcare professional may prescribe a T4 test in conjunction with other thyroid function tests, such as Thyroid-stimulating hormone and Triiodothyronine if the individual has symptoms of these conditions. A thyroid panel is another name for this set of examinations.
Hypothyroidism can cause the following symptoms:
- Hypothyroidism leads to fatigue.
- One of the most typical symptoms of thyroid disease is unusual weight gain.
- Hypothyroidism is associated with cold intolerance. The body’s processes slow down when the thyroid does not produce enough thyroid hormones.
- Muscle pains, tightness, and stiffness, especially in the shoulders and hips, are all symptoms of hypothyroidism. Joint stiffness and discomfort Swelling of the hands and feet’s tiny joints.
- The skin might be dry or rough.
- Hair loss or thinning of hairs on the scalp can be all over the body.
- Decrease heart rate.
- Irregular menses or the most prominent sign of severe hyperthyroidism is absent menstruation. Increased SHBG from too much thyroid hormone can impede ovulation. Short and light periods: Bleeding may be extremely light and brief.
- Low thyroid hormone levels can hinder an egg from being released from the ovary (ovulation), compromising fertility.
Hyperthyroidism is another prevalent thyroid condition:
- Palpitations, hyperkinesis, heat intolerance and emotional lability are symptoms of hyperthyroidism.
- A sudden change in mood or emotional state.
- Heartbeats that are fast or irregular (Tachycardia and Arrhythmia).
- Constipation (because most hyperthyroidism patients acquire hypothyroidism while receiving therapy for the condition).
- Arousals from nervousness or irritability, as well as muscle weakness and constant drowsiness, can make it difficult to sleep. Night sweats and frequent urges to urinate, which can compromise sleep, could be triggered by an overactive thyroid.
- Hyperthyroidism can cause unintentional weight loss by speeding up the body’s metabolism.
Other reasons for a doctor to assess a patient’s T4 include monitoring the success of replacement thyroid hormone therapy, screening neonates for congenital hypothyroidism, and evaluating suspected hypothalamic or pituitary gland abnormalities.
Test results may differ depending on age, gender, medical history, test method, and other factors. It’s possible that the test results may not reveal a disorder.
Free thyroxine levels
- Free T4 levels in people should be between 0.8-1.8 nanograms per deciliter (ng/dL). A higher-than-normal amount of free T4 could indicate an overactive thyroid. Graves disease, an autoimmune disease, is one of the conditions linked to hyperthyroidism.
- Hypothyroidism can be diagnosed by abnormally low free T4 levels. This indicates that the thyroid gland isn’t producing enough hormones. An underactive thyroid (hypothyroidism) could be caused by an underlying disease such as Hashimoto’s disease, which is an autoimmune disorder.
Total thyroxine levels
In adults, a normal Total T4 level is between 5.0-12.0 grams per deciliter (g/dL).
T4 levels that are abnormally high could signify hyperthyroidism, thyroiditis, or goitre.
Hypothyroidism, a malfunction of the pituitary gland, starvation, iodine deficiency, or other illness can all trigger abnormally low T4 levels. This could lead to more Hashimoto’s thyroiditis investigations.