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Triiodothyronine, free

S -T3-V

The thyroid is a gland in the neck. It produces, stores, and excretes thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3). Thyroid hormones have several significant functions, and they are needed, for example, for hormone production (oestrogen) and hormone activity (growth hormone), fat, glucose and bone metabolism, as well as bowel, gall bladder, and liver function.

Triiodothyronine is mainly present in the body bound to proteins, and less than about one per cent is transported free in the bloodstream (S-T3-V). Thyroxine (T4) has four iodine atoms attached, and when one iodine atom is released in other tissues, it becomes triiodothyronine T3 (tri Greek for three, thyreos Greek for shield).

When is a good time to measure the T3-V value?

T3-V, or free T3 hormone, can be measured when investigating hyperthyroidism, if necessary. It can reveal early hyperthyroidism in a situation in which the thyroid-stimulating hormone (TSH) is low, but free thyroxine (T4-V) is normal. In addition, T3-V should be tested in connection with the following symptoms, which could indicate hyperthyroidism:

  • Trembling of the fingers
  • Intolerance to cold
  • Increased sweating
  • Fatigue
  • Nervousness
  • Weight loss
  • Increased appetite
  • Atrial fibrillation
  • Bulging eyes
  • Swelling and dryness around the eyes
  • Anxiety
  • Sleep problems
  • Weight loss
  • Weakness
What does a T3-V test measure?

The T3-V test indicates hyperthyroidism. The level of free T3-V hormone is examined when suspecting hyperthyroidism or monitoring previously diagnosed hyperactivity.

Normally, the result is: 

Reference values:

  • 2,6 - 5,7 pmol/l

The reference values of this examination have changed 11.10.2021. You will find your own result's reference values from My LOUNA in touch with the graph. Read more about defining reference values.

Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.

An elevated test result indicates hyperthyroidism (overactive thyroid). Hyperthyroidism means that the thyroid gland secretes higher amounts of thyroid hormones into the blood than normal, which emphasises their effects.

The onset of hyperthyroidism cannot be prevented or influenced through lifestyle changes. It is often caused by:

  • Basedow's disease (an autoimmune disease)
  • Multinodular goitre
  • A benign tumour (adenoma) of the thyroid gland

A severe chronic disease can lower the T3-V level.

  • Thyroxine, free, index of thyroid function (2836 S-T4-V)
  • TSH indicates thyroid disease (2832 TSH)
  • Thyroid peroxidase, antibodies are produced against the body’s own cells in an autoimmune disease (4028 S-TPOAb)
  • TSH receptor antibodies (4965 TSHRAb)

SYNLAB tests: Triiodothyronine, free https://www.yml.fi/tuotekuvaus_show.php?tuotenro=357

Suomen kilpirauhaspotilaat ry (Association of Finnish thyroid patients): Mikä on kilpirauhanen

Lab Test online: Thyroid function tests https://labtestsonline.org.uk/tests/thyroid-function-tests

Schalin-Jäntti C. Kilpirauhaspotilaan tutkiminen. Duodecim Terveysportti 28 January 2019.


Fasting is not required

This examination does not require fasting