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TSH - the lows and the highs – what does it reveal about your metabolism?

Are you having fatigue, changes in weight, intolerance to temperature changes and noticeable changes in various body systems? One of the reasons may be related to your body metabolism controlled by the thyroid gland. Thyroid hormones are highly essential for function of each cell in your body. They regulate the rate of chemical reactions or metabolism in the body, helping in growth and development.

What is TSH?

You might want to know about the origin of Thyroid stimulating hormone (TSH). TSH is produced by the pituitary gland in your brain after stimulation by another hormone called Thyrotropin-releasing hormone (TRH) from hypothalamus. TRH then triggers the pituitary gland to release TSH. TSH causes the thyroid gland to form two hormones: triiodothyronine (T3) and thyroxine (T4) which help control your body's metabolism.

TSH levels: the lows and the highs

The knowledge of the conditions which cause low and high TSH levels will help you to get an insight into the function of thyroid gland.

Low TSH levels

  • An overactive thyroid gland or hyperthyroidism. Causes of hyperthyroidism include Graves' disease, a type of goiter called toxic multinodular goiter or a noncancerous benign tumor called a toxic nodule
  • Excess consumption of thyroid medicine for treatment of an underactive thyroid gland
  • Damage to the pituitary gland that prevents it from making TSH in a condition called secondary hypothyroidism
  • Pregnancy during the first trimester

High TSH levels

  • An underactive thyroid or hypothyroidism. Hashimoto's thyroiditis is the most common cause of primary hypothyroidism
  • Inadequate consumption of thyroid hormone medicine for treatment of an underactive thyroid gland
  • A pituitary gland tumor that is making excess TSH which is uncommon

Uses of TSH test

It is beneficial for you to know about the uses of TSH testing. It is done to:

  • Detect the function of thyroid gland
  • Monitor the response in people taking thyroid replacement or anti-thyroid treatment
  • Detect an underactive thyroid gland in a newborn
  • Detect infertility issues in women and monitoring pregnant women
  • Evaluation of conditions such as obesity and depression 

Let us review the utility of TSH testing and importance of TSH levels:

Detection of function of thyroid gland

TSH testing detects whether your thyroid gland is overactive (hyperthyroidism) or underactive (hypothyroid). In case you have an overactive thyroid or hyperthyroidism, you can have symptoms such as weight loss, rapid heart rate, nervousness, diarrhea, a feeling of being too hot or irregular menstrual periods with low levels of serum TSH and high levels of serum T4. The serum TSH testing also identifies if you have subclinical hyperthyroidism. Subclinical hyperthyroidism is defined as a low-serum TSH concentration and normal serum T4 and T3 concentrations, in the absence of hypothalamic or pituitary disease, non-thyroidal illness or ingestion of drugs that inhibit TSH secretion such as glucocorticoids or dopamine.

Symptoms such as weight gain, tiredness, dry skin, constipation, a feeling of being too cold or frequent menstrual periods, usually point to an underactive thyroid gland or hypothyroidism. Your TSH levels can assist in detecting whether hypothyroidism is due to a damaged thyroid gland or some other cause such as a problem with the pituitary gland or the hypothalamus. Further, subclinical hypothyroidism is used to describe the finding of a raised TSH but a normal free T4 in cases of chronic autoimmune thyroiditis.

Monitoring the response to treatment

The response to treatment for thyroid dysfunction is monitored by TSH levels. It helps your physician to adjust the dose of thyroid medications accordingly and maintain your metabolism at an optimum level. In advanced cases where surgery which involves removal of part of your thyroid gland is followed by head and neck irradiation, it increases your risk of hypothyroidism. A study conducted to determine whether the incidence of hypothyroidism following radiotherapy to the low neck requires the routine monitoring of thyroid function in asymptomatic patients found out that head and neck irradiation results in biochemical hypothyroidism in at least half of patients. Hence, thyroid function should be tested on a regular basis every six month for the first five years following radiotherapy to the low-neck region.

Screening of newborns

In case, you are concerned about congenital hypothyroidism in your newborn, then neonatal screening can give you the solution. The TSH screening has become the standard in many parts of the world. It reveals information about the thyroid function and the need for thyroid replacement therapy in your newborn during the first three years of life to normalize the serum TSH concentration, ensuring optimal metabolism. If congenital hypothyroidism is not recognised, it can lead to mental retardation and developmental delay in newborns.

Detection of infertility issues in women

You may want to seek medical attention for your menstrual irregularities, infertility issues or miscarriages. The high and low levels of TSH both interfere with the normal functioning of the reproductive system. Studies have revealed that some patients with infertility and menstrual irregularities have underlying chronic thyroiditis or chronic inflammation of thyroid gland along with subclinical hypothyroidism. It has long been recognized that patients with overt hypothyroidism, thyroid hormone replacement therapy may normalize the menstrual cycle, restoring normal fertility and metabolism.

Thus, the Thyroid Stimulating Hormone test is the best screening test for conditions that can affect the thyroid gland. Your results will be evaluated by your physician based on your health and other factors. The physician will then consider any symptoms you might have along with other test results to determine if treatment is needed for restoration of your TSH levels.