T4 free

The role of free T4 (thyroxine) in the body

T4 free (FT4) is an inactive form of thyroid hormone produced by the thyroid gland. . It serves as the main ‘reserve’ from which active T3 (triiodothyronine) is formed in the tissues.

Key features:

1. Metabolism:

• Regulates basal metabolic rate(the rate at which calories are burned at rest).
• It affects the synthesis and breakdown of proteins, fats, and carbohydrates.

1. Energy balance:

• Supports body temperature and energy production.

1. Cardiovascular system:

• Increases your heart rate (HR) and sensitivity to adrenaline.

1. The nervous system:

• Provides normal brainfunction, concentration and memory.

1. Growth and development (in children):

• It is critically important for the formation of the central nervous system and bone system.

1. Reproductive health:

• It affects women’s menstrual cycle and fertility.

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Symptoms of free T4 deficiency (hypothyroidism)

Reasons:

• Autoimmune thyroiditis (Hashimoto’s disease).
• Iodine deficiency (endemic goiter).
• Surgery/radiation of the thyroid gland.
• Hypopituitarism (TSH deficiency due to pituitary gland problems).

Symptoms:

• Chronic fatigue, drowsiness, weakness.
• Chilliness, cold intolerance.
• Weight gain (swelling, slow metabolism).
• Dry skin, brittle hair and nails.
• Slow heart rate (bradycardia), low blood pressure.
• Constipation, bloating.
• Depression, memory loss, ‘fog in the head’.
• Cycle disorders in women, infertility.

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Symptoms of excess free T4 (hyperthyroidism)

Reasons:

• Graves ‘ disease (autoimmune hyperthyroidism).
• Toxic nodular goiter.
• Thyroiditis (inflammation with the release of hormones).
• Overdose of L-thyroxine.

Symptoms:

• Sharp weight loss(with increased appetite).
• Tachycardia, arrhythmia, sweating.
• Trembling hands, nervousness, insomnia.
• Diarrhea, frequent urination.
• Muscle weakness (especially in the shoulders and thighs).
• Exophthalmos (bug-eye in Graves ‘ disease).
• Violation of the menstrual cycle.

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Norm of free T4 in the blood test

Reference values depend on the laboratory, but on average:

* Translation: 1 pmol / l ≈ 0.078 ng / dl

Important:

• TSH level is the main marker for diagnosis (in hypothyroidism TSH ↑, in hyperthyroidism TSH ↓).
• T4 free is more accurate than total T4 (does not depend on the level of blood proteins).

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What should I do if there are deviations?

If T4 is lowered:

1. Check TSH (if TSH is high – primary hypothyroidism).
2. Pass antibodies to TPO and TG (if Hashimoto’s is suspected).
3. Replacement therapy with L-thyroxine (the dose is selected by the endocrinologist).

If T4 is raised:

1. Ultrasound of the thyroid gland (exclude nodules, inflammation).
2. Analysis for TSH receptor antibodies (TRAb) in Graves ‘ disease.
3. Treatment: thyrostatics (thiamazole), radioactive iodine, surgery.

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Conclusion

• Free T4 is the main ‘prohormone’ from which active T3 is formed.
• Deficiency leads to a slower metabolism (hypothyroidism).
• Excess causes acceleration of all processes (thyrotoxicosis).
• The FT4 norm is 12-22 pmol / L, but you need to interpret it together with TSH.