Free Thyroxine (T4 free)
Why this test?
For the diagnosis of the thyroid gland function disorders and control over their treatment.
To diagnose the causes of female infertility.
For the diagnosis of congenital hypothyroidism.
In what cases is it prescribed?
With symptoms of hyperthyroidism: rapid heartbeat, increased irritability, weight loss, insomnia, trembling hands, weakness, rapid fatigue, diarrhea (in some cases), increased sensitivity to light, impaired vision, swelling around the eyes, their dryness, redness, protrusion of the eyeballs apples.
With symptoms of hypothyroidism: weight gain, dry skin, constipation, cold intolerance, edema, hair loss, irregular menstruation in women.
With advanced hypothyroidism, complications such as heart rhythm disturbances, ischemia of the heart muscle, and coma may develop. In children, hypothyroidism sometimes causes a delay in physical and mental development - cretinism.
During a preventive (for example, annual) examination together with other laboratory tests (general analysis of blood and urine, various biochemical indicators).
To monitor the treatment of thyroid diseases - periodically together with the study of thyroid-stimulating hormone (at least once every 3 months).
Pregnant, prone to thyroid diseases or suffering from them - for timely detection of thyroid hormone secretion disorders (they can lead to termination of pregnancy or congenital pathology of the fetus).
In the first days of life, newborns born to mothers with thyroid diseases.
During the analysis, the concentration in the blood of the main thyroid hormone fraction - thyroxine (T4) – (that is not associated with proteins) is determined. This is one of the most important tests for evaluating the function of the thyroid gland, its results do not depend on the concentration of proteins that bind thyroxine in the blood plasma, and allow to detect the level of only the active part of the hormone. Most often, this test is prescribed together with the measurement of the concentration of thyroid-stimulating hormone (TSH) - the regulator of the function of the thyroid gland. The thyroid gland controls metabolism and the intensity of energy consumption by the body. It works according to the feedback mechanism with the pituitary gland. The pituitary gland secretes thyrotropin (TSH) in response to a decrease in the concentration of thyroxine (T4), thereby stimulating the thyroid gland to produce hormones. When the level of thyroxine increases, the pituitary gland begins to produce less thyroid-stimulating hormone and the secretion of thyroxine by the thyroid gland decreases.
Thyroxine (T4) makes up about 90% of the total amount of hormones secreted by the thyroid gland. In the blood, T4 is found either in free form or in the form bound to globulin proteins. The main part of all thyroxine is in bound form and only 0.1% is in free form. It is the free fraction of the T4 hormone that is the most biologically active.
If the thyroid gland is not able to produce the required amount of thyroxine or not enough thyroid-stimulating hormone is produced to stimulate it, symptoms of hypothyroidism appear. In patients with a reduced level of T4, body weight increases, the skin dries up, fatigue increases, they become very sensitive to cold, and in women the menstrual cycle is disturbed. If the level of free T4 is higher than normal, the metabolic processes in the body and the production of energy in the cells increase, which leads to hyperthyroidism, which is characterized by rapid heartbeat, anxiety, weight loss, sleep disturbances, tremors in the hands, dry and red eyes, puffy face.
The most common cause of thyroid hormone imbalance is autoimmune damage to the gland. This can be Based's disease (causes hyperthyroidism with an increased free T4) or Hashimoto's thyroiditis (causes hypothyroidism - free T4 is reduced).