Thyroxine free (T4 free)

Free thyroxine is a polypeptide that is free in the blood, and therefore it is active, thyroid hormone. However, its activity is 6-10 times weaker than that of another hormone - triiodothyronine. But thyroxine performs similar functions to triiodothyronine and has a very similar structure.

Hormone characteristics and functions

Thyroxine (T4) is synthesized in the tissues of the thyroid gland (thyroid gland). Free T4 is contained in the blood in a small amount - 0.02-0.04%. If there is no need for a precursor, then it is deposited in thyroid follicles. If free T4 is contained in the blood in an insufficient amount, then the body "gets" the thyroglobulin molecule, "cuts" it into the necessary parts and uses it in the metabolic processes:

·         stimulates processes occurring in some areas of the brain;

·         increases protein synthesis rate;

·         stimulates warmth and gas exchange;

·         changes strength and heart rate;

·         participates in tissue growth and differentiation;

·         influences contractility and muscle fatigue;

·         participates in the formation of resistance to stress and infections;

·         maintains a low level of lipids and cholesterol in the blood.

Important mission of the free T4 hormone is its contribution to the regulation of reproductive system processes.

Indications for the test

An analysis to determine the level of the free form of thyroxine is prescribed in case of:

·         differential diagnosis of thyroid pathology and to evaluate the effectiveness of therapy for hyperthyroid conditions;

·         condition control in isolated T3-toxicosis;

·         screening and differential research of the results of hormone replacement and suppressive therapy using thyroxine preparations;

·         deviations from the normal level of thyroid-stimulating hormone with normal activity of free T4;

·         manifestations of hyperthyroidism and the norm of free T4.

An immunochemiluminescent blood test is used to study the level of free thyroxine.

Preparation for the test and norms

The preparation includes the following stages:

·         stop eating before 8-10 hours;

·         reduce the consumption of fried and fatty food before 1-2 days;

·         limit harmful psycho-emotional influences;

·         exclude taking medicines;

·         avoid smoking.

The reference values of free T4 are:
Life periods

Free hormone rate (pmol/l)

Men

10,1-23,0

Children of various ages:

 

1 month

16-33

6 months

15-29

12 months

14-23

1-5 years old

13-23

6-10

12,7-22,2

11-15

12,1-22,0

Women

10,3-24,5

I trimester

12-19,6

II trimester

9,7-17

III trimester

8,5-15,6

 

A therapist or endocrinologist should interpret the results.

An increase in the level of thyroxine may be caused by:

·         hyperthyroidism of any etiology;

·         isolated T3-toxicosis;

·         Thyroid dysfunction after childbirth;

·         iodine deficiency;

·         obesity;

·         hemodialysis.

A reduced hormone occurs as a result of the manifestation of such pathologies:

·         thyroid resection;

·         hypothyroidism;

·         autoimmune thyroiditis;

·         effects of radioactive iodine injection into the gland.

How to take the test, you need to find out from the doctor in order to get objective results of the test.