Total Triiodthyronine (T3 total)

Why this test?

For diagnosis and monitoring of triiodothyronine-induced thyrotoxicosis and hypothyroidism.

In what cases is it prescribed?

When the level of TSH is reduced with a normal content of free thyroxine (T4). 

With symptoms of hyperthyroidism (thyrotoxicosis) and a normal level of free thyroxine. 

Symptoms of hyperthyroidism: rapid heartbeat, increased irritability, weight loss, insomnia, hand tremors, weakness, rapid fatigue, diarrhea, increased sensitivity to light, visual disturbances, puffiness around the eyes, dryness, redness, exophthalmos (bulging of the eyeballs) . 

Symptoms of hypothyroidism: weight gain, dry skin, constipation, cold intolerance, swelling, dryness, hair loss, irregular menstruation in case of women. 

With an asymptomatic increase in T4 (which can sometimes occur with euthyroidism, in such cases, the increase in thyroxine is associated with a change in the concentration of TSH).

Testing preparation 

Avoid taking steroid and thyroid hormones 48 hours before the testing (in consultation with the doctor). Avoid physical and emotional stress 24 hours before the testing. 

Test Information 

Triiodothyronine (T3) is a thyroid hormone, the biological activity of which is 3-5 times greater than the activity of thyroxine (T4). 

Some amount of triiodothyronine is synthesized in the thyroid gland, but mainly it is formed during deiodination of thyroxine outside it. 

Most of the triiodothyronine circulating in the blood is bound to plasma proteins, in particular to thyroxine-binding globulin, thyroxine-binding prealbumin, and albumin. The portion of triiodothyronine that remains (less than 1%) is the biologically active (free) fraction. 

Triiodothyronine regulates the rate of oxygen consumption by tissues, stimulates protein synthesis, gluconeogenesis and glycogenolysis (which leads to an increase in the concentration of glucose in the blood), lipolysis, intestinal motor function, enhances the catabolism and removal of cholesterol from bile, promotes the synthesis of vitamin A and the absorption of vitamin B12 in the intestine, bone growth, production of sex hormones. 

Children need this hormone for the growth and development of the central nervous system.