What causes changes in TSH and how is it controlled?

TSH is an essential hormone for metabolism, whose changes usually warn of some endocrine alteration. Can its variations be controlled? We analyze it.

Last update: 07 February, 2022

Thyroid hormones play a fundamental role in the regulation of the metabolism of human beings. The quantification of TSH, triiodothyronine (T3) and thyroxine (T3) allows early identification and control of thyroid gland disorders. But what causes changes in TSH? Next we tell you.

Thyroid-stimulating hormone (TSH) or thyrotropin is a substance released in the hypophysis or pituitary glandlocated at the base of the brain. Studies affirm that this protein hormone is the main regulator of thyroid function.

TSH is responsible for increasing or decreasing the secretion of T3 and T4according to the needs of the organism. In general, blood levels of TSH can guide the diagnosis of diseases such as hypothyroidism and hyperthyroidism.

How is TSH produced?

All circulating thyroid hormones are under the control of the hypothalamic-pituitary-thyroid axis. In this sense, the synthesis of TSH begins in the hypothalamus, a neuroendocrine structure that acts as an intermediary between hormones and the nervous system. To do this, the hypothalamus releases thyrotropin-releasing hormone (TRH).

Thus, TRH travels to the anterior pituitary and induces the release of TSH from thyrotrophic cells.. Once TSH is in the blood, it will reach the thyroid gland and stimulate the synthesis of T3 and T4. In addition, this will be in charge of orchestrating a dynamic process known as thyroid feedback.

The feedback works according to the levels of T3 and T4 circulating in the blood. When thyroid hormones are low, the pituitary will release more TSH and this will increase the synthesis of T3 and T4. On the contrary, when the latter are high, the pituitary will stop the release of TSH.

It is for this reason that when TSH levels are elevated, doctors suspect hypothyroidism. On the other hand, when they are low, the diagnosis is oriented towards hyperthyroidism.

Normal TSH values

TSH values ​​are estimated from blood samples and are measured in milliunits per liter (mU/L). Most research suggests that normal TSH levels are between 0.5 mU/L and 5 mU/L. However, this range may vary according to the age and health status of the person evaluated.

On the other hand, the American Thyroid Association recommends that TSH be maintained between 0.2 and 2.4 mU/L during the first trimester of pregnancy and less than 3 mU/L in the remaining trimesters. This, considering that changes in TSH could increase the risk of miscarriage.

The measurement of TSH values ​​during pregnancy has been progressively incorporated into medical practice.

Causes of elevated TSH levels

The Elevated thyrotropin is a result of poor production of thyroid hormones. However, these changes in TSH can be caused by other situations, depending on whether or not the person tested has a known thyroid condition.

primary hypothyroidism

Primary hypothyroidism is the most common cause of high TSH levels.. In this disease, the thyroid gland does not work properly, so there will be less release of T3 and T4. For this reason, the pituitary will increase the release of TSH in a compensatory way.

Studies affirm that this hormonal deficit affects 4 to 6% of the general population, being more frequent in older women. Family history, thyroid surgery, and radiation therapy increase the risk.

Antibody thyroiditis

Some autoimmune pathologies, such as Hashimoto’s thyroiditis, can cause elevated TSH titers. In these cases there will be an infiltration of antibodies in the thyroid tissueprogressively affecting its functioning.

Initially, TSH and thyroid hormone values ​​are normal, but after a while TSH will rise and TSH and thyroxine (T4) will fall. Affected individuals are usually hypothyroid.

Treatment result

An elevated TSH may be found in people who are being treated for thyroid disease. In the case of hypothyroidism, a high TSH could indicate the need to increase the dose of the replacement medication.

Similarly, malabsorption of dietary drugs, such as levothyroxine, can also induce changes in TSH. For this reason, it is vital to follow in detail the indications for use given by health professionals.

On the other hand, a high TSH in a person with hyperthyroidism usually means that the treatment is very effective. In this way, the exaggerated production of T3 and T4 would have been limited.

Causes of low TSH levels

In most cases, low TSH is associated with increased production of thyroid hormones. Similarly, the causes depend on the presence or not of some pathology.


Thyroid hyperfunction is the most common reason for low TSH. Research estimates a prevalence of hyperthyroidism ranging from 1.3 to 6% of the population. The most common causes include toxic nodules, goiter, Graves’ disease, and toxic adenoma.

Unlike hypothyroidism, changes in TSH in this condition are the result of overproduction of thyroid hormones. Diagnosis usually requires laboratory results of T4 and TSH.

central hypothyroidism

This is a rare form of hypothyroidism reflecting a dysfunction of the pituitary or hypothalamus in the release of TSH. In addition, it is common for there to be an imbalance in the functioning of other hormone systems. In central hypothyroidism, TSH and T4 are decreased.

Treatment result

In some cases, people with hypothyroidism may have low TSH values ​​due to a excessive use of hormone replacement drugs. Similarly, it is possible that certain foods can interact with replacement drugs.

In contrast, low TSH levels in a person with hyperthyroidism highlight the need to increase the treatment dose or improve the treatment plan. Additionally, these changes in TSH may signal the need for monitoring.

The doses of medications to treat thyroid pathologies are adjusted according to TSH results.


During pregnancy, elevated levels of the hormone human chorionic gonadotropin (hCG) can stimulate the release of thyroid hormones. This fact generates a reduction of TSH values ​​by feedback. This form of hyperthyroidism disappears from the second trimester.

Potential Factors Causing Changes in TSH Results

There are several factors that can cause changes in TSH results. In this sense, it should be considered that laboratory values ​​do not always reflect the real health status of people.

Some of the possible situations associated with bias are the following:

  • Laboratory failures: During the taking of the samples, there may be faults in the extraction and processing of the blood that condition changes in the TSH values.
  • Antibodies: Studies suggest that antibodies can cause errors in the accuracy of thyroid tests in 1% of cases.
  • Diseases: some pathologies are capable of reducing proteins and raising free T4 levels. Similarly, the results of the TSH would also experience changes.
  • Medicines: non-steroidal anti-inflammatory drugs (NSAIDs), aspirin and oral contraceptives (OCs) can stimulate an increase in free levels of thyroid hormones.
  • Diet: the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) suggests that iodine-rich foods and seaweed products can bias thyroid tests.
  • Insomnia: poor sleep quality is related to imbalances in the functioning of the thyroid.
  • Supplements: Taking supplements high in biotin has been found to interfere with thyroid hormone results.

How to control changes in TSH?

TSH levels are usually subject to the concentration of thyroid hormones. In this sense, the treatment of conditions of the thyroid gland usually compensates them.

Hormone replacement therapy is used in hypothyroidism. such as synthetic levothyroxine. These medications stabilize T3 and T4 levels.

On the other hand, in hyperthyroidism, different techniques are used to reduce the production of hormones. Some of the treatment measures include radioactive iodine, antithyroid drugs, and surgical removal of the thyroid.

TSH and T4 tests are the gold standard for diagnosing diseases of the thyroid gland. Changes in TSH values ​​are often suggestive of hypothyroidism or hyperthyroidism.

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