Triiodothyronine (T3) Free
Triiodothyronine (T3) is one of the thyroid hormones. Its concentrations in the blood are lower compared to thyroxine (T4), but its activity is several times higher. The active substance is partially formed in the thyroid gland and partially in the liver and kidneys when thyroxine is broken down. Most of the hormone circulates in the blood in an inactive complex with transport proteins, and only 0.3% of its amount affects body tissues.
Under the influence of T3, there is active oxygen consumption by cells, increased breakdown of fats and carbohydrates, as well as protein synthesis. Triiodothyronine stimulates bone growth, synthesis of sex hormones, absorption of vitamins in the intestines, and also participates in the development of the central nervous system in children.
Synonyms: Free triiodothyronine, Free T3, FT3, free T3.
Indications for analysis assignment:
- Symptoms of hyperthyroidism: increased body temperature, blood pressure, heart rate, trembling hands, weight loss with good appetite, excessive excitement, insomnia.
- Symptoms of hypothyroidism: lethargy, sluggishness, drowsiness, puffiness, weight gain when there is a loss of appetite, low blood pressure, decreased heart rate.
- Changes in T4 and TSH levels in the blood.
- During treatment of hyperthyroidism or hypothyroidism to monitor treatment effectiveness.
Analysis description:
The enzyme-linked immunosorbent assay method is used to evaluate the hormone level. Taking a blood sample from the patient is required.
Preparation for the test:
To ensure maximum accuracy and benefit of the analysis results, it is recommended to refrain from taking medications containing steroids or thyroid hormones (only with the approval of the treating physician) for 48 hours before the test. Avoiding alcohol, stress, and exercise for 48 hours before the test is also advised. Fasting for 5-8 hours before the test (only pure water is allowed to drink), and refraining from smoking for 3 hours are necessary.
Result interpretation:
Measurement units: picomoles per liter (pmol/L).
Normal concentration: The normal level of free triiodothyronine ranges from 3.1 to 6.8 picomoles per liter.
Analytical result:
Excess free triiodothyronine may be evident in the following conditions:
- Hyperthyroidism (thyrotoxicosis).
- Thyroiditis – thyroid inflammation.
- Thyroid cancer.
- Iodine deficiency.
- Nodular goiter.
- Pendred syndrome (an inherited disorder characterized by hearing loss, balance disturbances, and thyroid gland involvement).
The hormone level also increases with the intake of radioactive iodine medications, estrogen, thyroxine, and some anti-tumor drugs.
A deficiency of free triiodothyronine may result from the following conditions:
- Hypothyroidism (hypothyroidism).
- Reduced thyroid function.
- Acute or early stages of organ inflammation.
- Previous surgery, severe injury, or illness.
Medications that decrease free T3 levels include antiarrhythmic drugs, anabolic steroids, some antiepileptic drugs, antihypertensive drugs, thyroid inhibitors, and lithium.
Additional tests when deviating from the norm:
In case of discovering an increase or decrease in free triiodothyronine, a comprehensive evaluation of thyroid function is required. Tests may include total T3, free T4, TSH and its antibodies, and thyroperoxidase antibodies. It may also require consultation with an endocrinologist, thyroid ultrasound imaging, basic blood and urine tests, and a series of other tests as needed.