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Triiodothyronine (T3) is a hormone produced in the follicular cells of the thyroid gland (50% of total hormone production) and in peripheral tissues as a result of thyroxine conversion (the remaining 50%). This hormone is tested when you suspect that you have an underactive or overactive thyroid gland.
Triiodothyronine (T3) – characteristics
Triiodothyronine is a hormone produced in the follicular cells of the thyroid gland. However, half of this hormone is secreted from thyroxine in target tissues. His examination is an action confirming or excluding hyperthyroidism / hypothyroidism. In addition, T3 is one of the most important thyroid hormones, whose special role takes place in unborn children during the development of the nervous and skeletal systems. This hormone also affects other processes in the human body, for example:
- water balance,
- energy transformations,
- fat metabolism,
- carbohydrate metabolism,
- protein metabolism,
- the functioning of the reproductive system,
- the functioning of the digestive system and circulation,
- the functioning of the kidneys.
What are the indications for the T3 test?
The most common indications for a triiodothyronine (T3) test include:
1. Suspicion of thyroid disorders – hypothyroidism and hyperthyroidism. The test is performed when the determination of T4 and TSH are not sufficient to make a diagnosis.
2. Presence of thyroid nodules.
3. Monitoring the treatment of thyroid diseases.
4. Diagnostics of thyrotoxicosis, ie a condition in which an excess of thyroid hormones causes symptoms suggesting an overactive thyroid gland.
5. Abnormal TSH test result.
The course of the study of triiodothyronine (T3)
For the credibility of the test, the determination of fT3 (free hormones) should also be performed. More than 99% of the hormone is present in the patient’s blood, while the remainder is spread throughout the body. For this reason, the T3 test is divided into two steps. First, any additional building blocks and elements in the blood are isolated from a blood sample taken from a vein in the arm. The next step is to introduce antibodies into the “purified serum”, which radiate in addition to binding T3 molecules. The hormone level is determined by the light intensity generated.
Material for T3 test: serum.
Preparation for the test: on an empty stomach (at least 8 hours).
The course of the study: one-time blood sampling from a vein in the arm.
Waiting time for the T3 result: 1 Day.
Standards: Total tridothyronine (T3) 1,5-2,9 nmol / l; Free triiodothyronine (fT3) 3,15–5,61 pmol / l
Comments: Most triiodothyronine is bound to serum proteins (albumin, prealbumin, thyroxin-binding globulin). Only 0,3% of the total amount of triiodothyronine remains unbound (free fraction) and exhibits physiological effects. The functioning of triiodothyronine is 3 to 8 times stronger than that of thyroxine. T3 is the main thyroid hormone that functions at the tissue level. It is largely responsible for the effects of thyroid hormones.
T3 hormone test result
The concentration of carrier proteins depends on many factors, e.g. medications, pregnancy, liver diseases and kidney diseases. For this reason, the test result should be consulted with a specialist in each case.
Triiodothyronine T3 above normal means: hyperthyroidism or nodular goitre. Another reason is taking preparations containing the T3 hormone. However, a result that is below normal indicates hypothyroidism (eg Hashimoto’s) or subacute thyroiditis.