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Free thyroxine (T4-Free) or tetraiodothyronine is a thyroid hormone
Thyroxine is a hormone secreted by the thyroid gland. If there is too little thyroxine in the body, the condition is called hypothyroidism. If the thyroxine level is high, the condition is called hyperthyroidism.
Free thyroxine T4-Free
- Thyroxine is a hormone secreted by the thyroid gland.
- Hyperthyroidism is a condition in which the amount of thyroxine in the blood is high.
- Conversely, hypothyroidism refers to a situation in which it is low.
- The thyroid affects the body’s metabolism.
Thyroxine T4
Thyroxine is one of the two important thyroid hormones. The thyroid regulates the entire body’s metabolism.
The thyroid is a gland weighing about 20 grams and it is located in the neck. Its overactivity or insufficiency may cause various symptoms in the body.
What is free thyroxine T4?
Thyroxine (or tetraiodothyronine) is one of the important thyroid hormones in addition to triiodothyronine. Thyroxine amounts to more than 80 per cent of the thyroid hormones in blood.
Free thyroxine is not bound to transporter proteins. Thyroxine is a derivative of the amino acid tyrosine. It contains four iodine atoms.
Most of the thyroxine circulating in the body is bound to transporter proteins. The total amount of T4 depends on the amount of transporter proteins.
In hypothyroidism, the amount of thyroxine in the blood is lower than normal and, conversely, in hyperthyroidism it is higher than normal.
In addition to the T4 study, the amount of thyroid stimulating hormone (TSH) secreted by the pituitary gland can be analysed.
What are the reference values for free thyroxine P-T4?
The reference values for free thyroxine P-T4 for all people are 12–22 pmol/l (picomoles per litre).
The reference values vary from laboratory to laboratory and according to the analysis method.
The analysis can be misrepresentative due to a rheumatoid factor, albumin binding abnormalities, heparin therapy and T4 antibodies.
High T4, free thyroxine
Free thyroxine may also be high due to reasons other than actual thyroid dysfunction. All of the following conditions and situations may cause free T4 to rise:
- Hyperthyroidism is diagnosed if other tests also suggest it and the patient develops symptoms indicative of it.
- The postpartum period may cause the values to rise. In this case, the test should be repeated after some time so that the body has time to recover. The value may decrease on its own over time or the condition may develop into hyperthyroidism.
- Certain medications may increase the values.
- Diseases that involve an increase in free fatty acids may also increase the amount of free T4.
Low T4, free thyroxine
Hypothyroidism decreases the amount of free T4.
Why is free thyroxine T4 studied?
When examining hyperthyroidism or hypothyroidism, the amount of free thyroxine should be studied as its concentration is less affected by the amount of transporter proteins. This provides a more accurate picture of the function of the thyroid gland.
The overall level of thyroxine is more influenced by the amount of transporter proteins, which can be analysed with a separate test.
Free thyroxine should be studied if symptoms of thyroid dysfunction occur. Typical symptoms of hyperthyroidism include weight loss, rapid heartbeat and sweating. Typical symptoms of hypothyroidism are weight gain, slow pulse, fatigue and general poor condition.
Potential insufficiency in newborns is automatically checked as a standard procedure as failure to treat it can lead to serious health problems.
Determining the amount of free T4 is important, especially if other concentrations that may indicate thyroid problems, such as TSH, are within the reference values or there are inconsistencies in the interpretation of their results.
FAQ
Hypothyroidism is treated with thyroxine replacement therapy, which means that the patient is given synthetic thyroxine (T4) to replace the missing hormone. The treatment is adjusted individually to the patient’s needs, and the effectiveness of the treatment is monitored with regular blood tests that measure the levels of thyroid hormones. The treatment is usually lifelong.
A thyroid test is taken when there is a suspicion of thyroid dysfunction or to monitor an already diagnosed thyroid disease.
Thyroid levels can change in a few weeks, but usually, the changes occur more slowly, over months.
A thyroid test is taken as a blood test.
Hypothyroidism usually develops slowly, often over several years.
Hypothyroidism can cause symptoms such as fatigue, weight gain, intolerance to cold, constipation, and dry skin.
Thyroid medication is usually started when laboratory tests show abnormalities in thyroid hormone levels and the patient has symptoms.
The results of thyroid tests are usually available the 1-2 business days.
The frequency of thyroid tests depends on the patient’s situation. Typically, follow-up tests are done every 6-12 months, but they can be done more frequently to assess the response to treatment.
Hyperthyroidism is diagnosed in the same way as hypothyroidism: with blood tests that measure the levels of TSH and free T4. In hyperthyroidism, TSH is low and free T4 is high.
Thyroid disorders can cause a variety of symptoms such as fatigue, weight changes, mood swings, dry skin, and hair loss.
Hypothyroidism is diagnosed with blood tests that measure the levels of TSH and free T4. If TSH is elevated and free T4 is low, it indicates hypothyroidism.
The effects of thyroxine can start to appear within a few days, but the full effects may not be evident until several weeks or months later. This depends on various factors, such as dosage and individual differences in thyroid function.
Vital laboratory package Total Plus includes 37 values and is an even more comprehensive health check for those who seek a deeper insight into their body’s well-being and greater opportunities to make better choices to improve their health.
1290 kr
Vital laboratory package Total includes 29 values and is a great choice when you want to gain more thorough information about the well-being of your body.
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T4, or thyroxine, is a thyroid hormone and its level indicates the activity of the thyroid gland.
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Thyroid-stimulating hormone (TSH) is a hormone that regulates thyroid function
TSH or thyroid-stimulating hormone is secreted by the pituitary gland. TSH is tested when examining thyroid function.
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Article updated:
23 October 2024