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T3 (triiodothyronine) is an active thyroid hormone.

T3 (triiodothyronine) is an active thyroid hormone

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.

Brief about T3 (triiodothyronine):

  • T3 is an active thyroid hormone needed to regulate the body’s metabolism.
  • Thyroxine (T4) is converted into the more active triiodothyronine (T3) in the body.
  • Free T3 is often examined when thyroid diseases are suspected, especially in cases of suspected hyperthyroidism.

What is T3 (triiodothyronine)?

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.

What are the reference values for T3?

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.

What does a high T3 value mean?

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.

What does a low T3 value mean?

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.

Why is T3 tested?

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.

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