fT4 test

It is a blood test performed to determine the concentration levels of a thyroid hormone known as free thyroxine. Free thyroxine (fT4) plays an important role in regulating metabolism, e.g. in the process of glucose absorption.

What is the ft4 test

The test is used to assess the functioning of the thyroid gland. The functioning of the thyroid gland is controlled by the pituitary gland, which secretes the thyroid-stimulating hormone (TSH). It stimulates the thyroid gland to secrete free thyroxine (fT4) and free triiodothyronine (fT3). Determining the level of this hormone is necessary in the diagnosis of thyroid diseases.

Elevated fT4 levels

The causes of elevated fT4 values include:

• iodine-induced hyperthyroidism (earlier than fT3),
• early stages of Hashimoto’s disease,
• treatments with high doses of thyroxine.

Lowered fT4

The causes of lowered fT4 values:

• hypothyroidism,
• thyroiditis,
• post-strumectomy states (after thyroid excision),
• patients after radiotherapy,
• thyreostatic treatment.

fT4 results

Falsely elevated results may be caused by:

• high concentrations of the thyroxine-binding protein,
• drugs (amiodarone, heroin, methadone, contrast agents).

Falsely decreased values are caused by drugs (androgens, carbamazepine, diazepam, heparin, beta blockers, and rarely – autoantibodies).

Why should the thyroxine (fT4) hormone be regularly checked?

• The test is usually performed in individuals with suspected hypo- or hyperthyroidism..
• Individuals with thyroid hypertrophy, known as goitre, should also regularly check their fT4 levels.
• The free thyroxine (fT4) test is also performed in the diagnosis of thyroid cancer, autoimmune diseases and causes of infertility in women.

Go to the next tab to check the symptoms of hyper- and hypothyroidism.

Hypothyroidism – symptoms

• Fatigue,
• Feeling cold despite high outside temperatures,
• Muscle stiffness and pain in the joints,
• Lack of appetite and the accompanying increase in body weight and mass
• Dry skin and hair,

Hyperthyroidism – symptoms

• Feeling of heat and high perspiration,
• Nervousness, restlessness, irritability,
• Losing weight, despite increased appetite,
• Weakening,
• Ophthalmic symptoms – protrusion of the eyeballs, double vision, oedema and reddening of the eyelids or conjunctivae (typical of Graves-Basedow disease),
• Dyspnoea,
• Irregular menstruation in women,

The fT4 test is indicated in the case of suspected thyroid diseases, when the TSH concentration levels are out of the normal range (too high or too low).

It is extremely important to diagnose hypothyroidism in women planning to become pregnant as the deficiency of thyroid hormones is very detrimental for both the mother and the foetus.

Thyroxine test

• The test involves the collection of blood according to the standard procedure of blood collection (disinfecting the skin, putting on a tourniquet and applying pressure in the collection site – after the blood collection procedure is over, it is necessary to compress the injection site with a gauze square for 5 minutes, with the arm kept straight).
• The blood collection takes from a few to a few dozen seconds.
• No special preparation is required for the test.
• Blood should be collected in the morning.

fT4 Results

• Test results are usually available within 1 working day,
• It is possible to collect them at the reception desk of a selected centre,
• The results can be accessed online. For this to be possible, it is necessary to collect a password at the reception desk of a selected centre.