Thyroid Function Test
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Thyroid Function Tests

The thyroid function test is a blood test which checks the level of the hormones made by your thyroid gland and the levels of a hormone (TSH thyroid stimulating hormone) made by the pituitary gland in your brain. These two hormones finely balance the right amount of thyroxine production in the thyroid gland to maintain healthy bodily functions.

This is called a feedback loop: if the thyroid gland makes too much thyroxine it will feed back to the brain to make less TSH.

Thyroid disorders affect women 15 times more than men. A thyroid function test is at times necessary to determine whether any symptoms you may be experiencing are an indication of an underlying thyroid disorder.


Same day appointments, as much time as you need with the doctor and instant referrals to our network of Consultant Specialists.

If you are experiencing health concerns, you don't have to wait any longer.

If your TSH is low and your thyroxine level is high, you may have an overactive thyroid gland and if your thyroxine level is low and your TSH is high, you may have an underactive thyroid gland.

A thyroid function test will determine the levels of the two hormones in your blood.

If you notice any of the following symptoms, you may be useful to have a thyroid function test to rule out problems with your thyroid levels.

Hyperthyroidism Signs

  • Restlessness, difficulty sleeping, nervous, emotional and irritable.
  • Hand tremors.
  • Losing weight despite an increased appetite.
  • Heart palpitations.
  • Shortness of breath.
  • Feeling tired all the time and muscle weakness
  • An increased thirst, sweating and always feeling hot.
  • Diarrhoea or needing to go more often.
  • Hair thinning and itchy skin.
  • Menstrual periods light or infrequent.
  • A swelling of your thyroid gland (goitre) in the neck.
  • Eye problems if you have Graves' disease.

Signs of hypothyroidism

Basically, many body functions slow down.

  • Tiredness
  • Weight gain.
  • Constipation.
  • Muscle aches and pains.
  • Feeling cold.
  • Scaly dry skin
  • Lifeless hair.
  • Fluid retention.
  • Mental slowing.
  • Depression.

Less common symptoms include:

  • Hoarse voice.
  • Irregular or heavy menstrual periods in women.
  • Infertility.
  • Loss of sex drive.
  • Carpal tunnel syndrome (which causes pains and numbness in the hand).
  • Memory loss or confusion in the elderly.

Understanding the Thyroid Function Test

A thyroid function test is a series of blood tests measuring how well the thyroid gland works. These tests include TSH, T3, T4, and T3RU.

A doctor who may be concerned about the hormone levels of your thyroid will order a blood screening test including the above. If these results are inconclusive, further investigations will be done to determine the cause.


Same day appointments, as much time as you need with the doctor and instant referrals to our network of Consultant Specialists.

If you are experiencing health concerns, you don't have to wait any longer.

Thyroid Function Test Procedure

Preparing for the Test

Prior to the blood test make sure that you have had plenty to drink. It makes taking blood easier.

During the Test

A needle will be inserted into a vein in your arm near your elbow, you may feel a slight scratch or prick and a small amount of blood will be taken for analysis.

T3 Results

The T3 test will identify the levels of triiodothyronine. This test is concludes if you have an overactive thyroid gland or your TSH and T4 are low.

T3RU Results

A T3RU test measures the binding capacity of your thyroxin-binding globulin (TBG). Low levels of TBG indicates a problem with your kidney or your body is getting insufficient amounts of protein while high levels of TBG indicate high levels of oestrogen in your body.

TSH and T4 Results

The TSH test determines the amount of thyroid-stimulating hormone in your blood and the T4 test measures your thyroxine levels. A normal range for the TSH test is between 0.4 and 4.0 mIU/L.

If you have a family history of acquired thyroid dysfunction, it is recommended you undergo a thyroid function test. This way, you can be sure your thyroid and bodily functions are healthy especially if you are experiencing unexplained symptoms of feeling unwell or out of sorts.



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At Walk in Clinic, we provide convenient and affordable private gp services to patients. If you are staying, visiting or working in London, then our gp appointments can be conducted in person by walking in at the clinic.