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Thyroid-Stimulating Hormone or TSH is a hormone produced by the pituitary gland that stimulates the thyroid gland. Measuring the TSH levels is considered the best way to diagnose the thyroid disorders. It is also called Thyrotropin.

Historical background of TSH researches

The history of TSH researches began with the discovery of thyroid-stimulating activity in the pituitary gland. At the beginning of the last century, it was demonstrated that the anterior lobe of the pituitary gland secretes some kind of thyroid stimulator. These initial findings were followed by the experiments on the purification and determination of the primary structure of the TSH subunits.

Synthesis and regulation of TSH

The quantity of thyroid hormones in the bloodstream is monitored and controlled by the pituitary gland and TSH. This hormone is being synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. The more circulating TSH, the more thyroid hormones are being produced. It all starts with the hypothalamus, the gland that produces Thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release TSH.

Then TSH stimulates the thyroid gland to secrete the following hormones:

  1. Thyroxine (T4) and
  2. Triiodothyronine (T3).

This entire regulation procedure is well studied and scientists have proved that it is following a precise mechanism called negative feedback mechanism. It means that the production of TSH is inhibited by the production of one other hormone called Somatostatin by the hypothalamus. T3 and T4 also inhibit TSH production and secretion, creating a regulatory negative feedback loop.

Chemical structure of TSH

When we talk about the chemical structure of the Thyroid-Stimulating Hormone, we should know that it consists of two subunits, the alpha and the beta subunit.

  • The alpha subunit is chemically identical to human chorionic Gonadotropin hormone, luteinizing hormone and follicle-stimulating hormone.
  • The β (beta) subunit determines the function of the hormone.

TSH is a member of the glycoprotein hormone family, which is structurally classified as a part of the CKGF super-family of structurally related proteins with very important biological activities.

TSH and thyroid disorders

Measuring the level of TSH in the blood is probably the best possible way to diagnose all disorder associated with the thyroid gland. The thyroid gland is a butterfly-shaped gland, located at the front part of your throat just below your Adam's apple. Why is the thyroid gland so important? This small gland is producing hormones that affect and regulate virtually every bodily function. Triiodothyronine (T3) and Thyroxine (T4) are also needed for normal development of the brain, especially during the first 3 years of life. This is why; a child whose thyroid gland does not produce enough thyroid hormone may become mentally retarded.

They control:

  1. metabolism and organ function, directly affecting weight loss or gain,
  2. energy levels,
  3. skin condition,
  4. memory,
  5. heart rate,
  6. cholesterol levels,
  7. menstrual regularity,
  8. memory as well as many other functions.

So, it is logical to assume that, if a thyroid gland is not working properly, a variety of possibly severe medical problems may occur.

The goals of thyroid disease treatment

The goal of treatment for any thyroid disorder is to restore normal blood levels of thyroid hormone. When it comes to hypothyroidism, it is usually treated with a drug called Levothyroxine. This is, in fact, a synthetic hormone that is used to replace the missing thyroid hormones in the body. There were a lot of experiments and theories regarding synthetic TSH production and its’ applying on the patients. It would enable the increased production of thyroid hormones but the good results were not secured. Hyperthyroidism, which is generally more difficult to treat, requires the normalization of thyroid hormone production. It is treated with anti-thyroid medications and the most common is the radioactive iodine.

TSH blood test

A thyroid-stimulating hormone blood test is a simple test that is being used to detect problems affecting the thyroid gland. The good side of this test is that it provides an accurate, convenient, and inexpensive way to discover TSH level. The procedure is rather simple. A blood specimen collection process is quick, easy and virtually painless. A special lancet is being used to break the skin and make a small lesion on the nick of a finger. After that, a few drops of blood are taken and deposited into a special collection device which is then being sent to a laboratory for an analysis.

Normal TSH blood test results

The values of TSH in the blood can vary but the following values are considered as normal:

  1. Newborns: 3–20 milli-international units per liter (mIU/L)
  2. Adults: 0.4–4.5 milli-international units per liter (mIU/L

T3

T4

TSH

Interpretation

Normal

Normal

High

Mild hypothyroidism

Low or normal

Low

High

Hypothyroidism

Normal

Normal

Low

Mild hyperthyroidism

High or normal

High or normal

Low

Hyperthyroidism

Low or normal

Low or normal

Low

Rare pituitary (secondary) hypothyroidis

High values of measured THS test might indicate:

  1. An underactive thyroid gland caused by the failure of the thyroid gland – a condition called primary hypothyroidism.
  2. Pituitary gland tumor that is producing excess amounts of TSH.
  3. Underactive thyroid gland and ise receiving too little thyroid hormone medication.

Low values of measured THS might indicate:

  1. overactive thyroid gland - a condition called hyperthyroidism
  2. damage to the pituitary gland that prevents it from producing TSH
  3. Underactive thyroid gland that is receiving too much thyroid hormone medication.

Indications for the TSH blood test

A test of the thyroid-stimulating hormone levels is definitely the best test if you want to determine whether the thyroid gland is functioning properly.

TSH testing is used to:

  • diagnose a thyroid disorder in a person with symptoms,
  • screen newborn kids for an underactive thyroid,
  • monitor thyroid replacement therapy in people with hypothyroidism
  • diagnose and monitor female infertility problems,
  • Help evaluate the function of the pituitary gland- A low TSH may ocasionally result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid. This condition is called secondary hypothyroidism.

Increased or decreased thyroid hormone results indicate that there is an imbalance between the body’s requirements and supply. The thyroid gland can either be overactive and underactive.

An underactive thyroid is the most common thyroid disorder and this condition is called the hypothyroidism. The most common symptoms of this condition are:

  • weight gain,
  • tiredness,
  • dry skin,
  • constipation,
  • a feeling of being too cold,
  • Frequent menstrual periods,
  • Forgetfulness,       
  • Muscle cramps,     
  • Edema.

An overactive thyroid (hyperthyroidism) can cause symptoms such as:

  • weight loss,
  • rapid heart rate,
  • nervousness,
  • diarrhea,
  • Insomnia,
  • Tremor
  • a feeling of being too hot,
  • Irregular menstrual periods.

It is a very important fact that the amount of TSH present in the blood is directly related to both hyperthyroidism and hypothyroidism.

It is not difficult for a doctor to determine that the patient has problems with hypothyroidism but, the TSH levels measured by this test can’t help determine whether hypothyroidism is due to a damaged thyroid gland or some other cause.

Other problems that can cause this condition are the problems with the pituitary gland or the hypothalamus. Many patients diagnosed with hypothyroidism are on hormone replacement therapy and in these cases monitoring the condition by performing regular TSH tests is very quick, practical and useful.

Thyroid-stimulating hormone suppression therapy

Thyroid-stimulating hormone suppression therapy is a pretty new and effective therapy whose goal is to reduce the amount of the thyroid-stimulating hormone in the body.

Indications for TSH suppression therapy

The TSH suppression therapy is indicated in conditions such as:

  • Post-operative treatment of thyroid cancer - because the treatment will reduce the TSH in body and help prevent the growth of any remaining cancer cells.
  • Thyroid cancer or a suspicious nodule is present but the patient isn't healthy enough to have a surgery.

The bottom line is that this suppression therapy is being used because it is considered that when the body makes less TSH, there is less thyroid growth and perhaps less nodule growth.

Read More: Thyroid Symptoms and Problems in Women

Contraindications

  1. It is not recommended for people who are older than 60 or for women that entered the menopause period
  2. TSH suppression therapy can increase the risk of heart and bone problems, especially if the patient already has a heart disease or osteoporosis
  3. It is also contraindicated when used along with some other medications such as:
  • cholestyramine, ferrous sulfate (iron), sucralfate, and some antacids that contain aluminum hydroxide
  • seizure medicines
  • anti-tuberculosis medications
  • lithium,
  • potassium iodide,
  • amiodarone,
  • dopamine, and
  • Prednisone.

Side effects of TSH suppression therapy

TSH suppression therapy can cause many side effects and some of the most common are:

  1. Diarrhea
  2. Weight loss
  3. Headache
  4. Changes in appetite
  5. Excessive sweating
  6. Anxiety or irritability
  7. Difficulty falling asleep or staying asleep

  • en.wikipedia.org/wiki/Thyroid-stimulating_hormone
  • www.labtestsonline.org