The hormone triiodothyronine, commonly known as T3, is produced in the thyroid gland and helps regulate metabolism throughout the body. The level of T3 in the blood is usually tested when examining the thyroid, especially when conditions such as hyperthyroidism are suspected.
The thyroid gland is located in the front of the trachea and produces hormones including thyroxine (T4) and triiodothyronine (T3). Primarily, T4 is produced, but it is converted into the more active T3 in the body’s cells.
T3 regulates the body’s metabolism, making it crucial for overall health. It is essential for the body’s protein synthesis and a deficiency in the hormone can lead to symptoms like fatigue and a general feeling of illness.
Only a small portion of T3 in the body is free in the blood and is called free T3; the rest is bound to various carrier proteins. In conditions such as hyperthyroidism, the production of T3 significantly increases, leading to symptoms like palpitations, insomnia, and nervousness.
The reference values for T3 in adults range between: 3.1 – 6.8 pmol/L.
These reference values may vary slightly between different laboratories and depending on the analysis method used.
High T3 values are usually indicative of hyperthyroidism. In this condition, the thyroid gland is overactive and produces an excess of thyroid hormones, which can lead to symptoms like palpitations, insomnia, and nervousness.
Low values are usually indicative of hypothyroidism, where the thyroid gland does not produce enough thyroid hormone, leading to symptoms like fatigue, weight gain, and a general feeling of illness. Low T3 values can also be due to other illnesses.
Testing of free T3 levels is primarily done when hyperthyroidism is suspected, and when other blood tests like TSH and T4 cannot confirm the diagnosis. Free T3 levels can also be used to diagnose hypothyroidism, but other markers are often better since T3 levels can remain normal for long periods despite hypothyroidism.
In summary, free T3 is rarely the first choice when examining thyroid health, but it is valuable in unclear cases. Free T3 is also typically examined during thyroid cancer treatment as it provides a good indication of treatment progress.
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 Woman 50+ includes 39 values and provides senior women with a broad overview of their health. Vital’s doctors have developed this laboratory package based on some of the most important values that affect age-related lifestyle diseases, as well as values that are interesting to monitor specifically for you as a woman over 50 years old.
Free T3 (Triiodothyronine) is an active thyroid hormone. Free T3 is usually measured in addition to TSH and Free T4 to diagnose any potential thyroid disorder.
TSH or thyroid-stimulating hormone is secreted by the pituitary gland. TSH is tested when examining thyroid function.
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.
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Article updated:
23 October 2024