What Low TSH or High TSH Levels Could Mean

Think of your thyroid gland as a clearinghouse in which information runs in and out, to make sure your entire body achieves the balance of homeostasis.

Thyroid stimulating hormone (TSH) is produced by your brain’s pituitary gland and sent to your thyroid, to make sure that a state of equilibrium known as homeostasis occurs.

TSH tells your thyroid to produce more or fewer hormones, specifically triiodothyronine (T3) and thyroxine (T4), to make sure you’re operating optimally. These two hormones regulate many important aspects of your body, including metabolic rate, body temperature, and brain development.

Because the right amounts of T3 and T4 are responsible for helping maintain a smoothly functioning body in so many ways, understanding high, low, and normal levels of TSH is vital.

What Is Homeostasis?

Homeostasis and the endocrine system are based on a negative feedback system. When any end organ produces a hormone, these hormones then make their way back to the hypothalamus and the pituitary gland, so that the brain and pituitary gland know there’s an adequate amount of hormone being made.

If one of these organs is damaged, such as in autoimmune thyroid disease, and the thyroid gland is no longer making an adequate amount of thyroid hormone, this lower level is then detected by the hypothalamus in the brain. Therefore, a large amount of TSH is released in an attempt to produce more thyroid hormone from the thyroid gland.

What to Know About TSH Levels

Most commonly, providers use TSH levels to guide therapy to ensure that a person is producing the right levels of thyroid hormone. It’s important to look not only at TSH test results, but also free T4 and total T3, which could provide more accurate numbers and present a more comprehensive picture of what’s going on and for your doctor to figure out the right treatment plan.

In addition to blood tests, it’s important that your doctor knows the full picture of your presenting symptoms and when they occur, plus any medications or supplements you may be taking. To get to the bottom of what your issue may be, it’s possible that your doctor may order further tests, including a thyroid ultrasound.

Since TSH is responsible for the creation of hormones T3 and T4, which help regulate so much of your body, and because there are so many factors at play in creation or suppression of these hormones, using TSH data serves as the beginning of any thorough diagnosis and treatment plan. It can be confusing, especially considering what’s really a normal range for one person is not for another, and that levels will shift for many reasons.

For example, Joseph Winchell, M.D., family medicine physician at Mount Carmel Medical Group in Pickerington, OH, references a situation in which suppressed TSH is shown via testing. The physician’s initial reaction would be to reduce therapy. However, after checking free T4 or total T3, the full picture shows levels in the normal range.

What are Normal TSH Levels?

It’s an ongoing debate. Ultimately, the standard of care is to treat into the goal range for TSH, which is typically between 0.5 and 4.5 or 5.

A TSH level of 10 mIU/L or higher is typically indicative of hypothyroidism. A TSH level of 4.5 to 10 mIU/L is considered indicative of subclinical hypothyroidism.

If you visit your doctor complaining of thyroid issues, worried by symptoms such as fatigue and the inability to lose weight, it’s important to remember that, while thyroid function plays a role in both your energy levels and your ability to gain or lose weight, there are a lot of other factors that need to be considered.

Being tired all the time does not necessarily mean you have a thyroid condition, just as being cold does not automatically mean you have hypothyroidism. An inability to lose weight or gaining excessive weight does not mean your thyroid is abnormal. So while it’s appropriate to check in these situations, patients should realize there are a lot of other factors that could be going on, and a wider differential needs to be looked at when you’re having these concerns.

What Could High TSH Levels Mean?

Suffering from high TSH typically means one of two things, according to Dr. Winchell.

Hypothyroidism

The most common is an underactive thyroid gland, or hypothyroidism. If your thyroid is not producing enough thyroid stimulating hormone, your pituitary gland is going to release more TSH to try to get more T3 and T4 from the thyroid gland.

It’s a little tricky to wrap your head around, but having high TSH levels indicates low levels of T3 and T4.

High TSH Levels Symptoms

When a patient reports symptoms that include sudden weight gain, fatigue, low energy, irregular periods, or problems with sleep, it’s possible that this is because of high TSH. Because symptoms of having high TSH are also common symptoms for other conditions, the only way to know is to have a doctor provide a blood test to check your TSH levels.

Looking at cumulative symptoms over time is also valuable for helping reach a diagnosis.

Euthyroid Sick Syndrome

Another common diagnosis of high TSH comes from nonthyroidal illnesses, otherwise known as euthyroid sick syndrome. In this instance sick people, frequently those hospitalized in the ICU, are producing less T3 or T4 because of the illness that they’re suffering from.

What Could Low TSH Levels Mean?

Unlike high TSH, in which only a few conditions present themselves for relatively straightforward diagnoses, there are many reasons for low TSH. Low TSH means higher levels of T3 and T4 produced by the thyroid gland.

Graves’ Disease

The most common diagnosis is Graves’ disease, which triggers hyperthyroidism. Put simply, that means an overactive thyroid. In this autoimmune disorder, the thyroid becomes overactive because it is attacked by the body’s immune system.

Central Hypothyroidism

Another example is a syndrome called central hypothyroidism. In this case, your TSH may be low, but you’re considered to have hypothyroidism because of damage to the pituitary gland. In this example, the gland is not making enough TSH to adequately stimulate the thyroid gland to produce T3 and T4. It’s a bit of a challenge to diagnose, and there’s more work-up to figure it out.

Overmedication

Exogenous thyroid use could also lead to a diagnosis of low TSH. This can happen from either taking too much thyroid hormone replacement medication or from abusing thyroid hormone medication, which could lead to suppressed TSH.

Notes: This article was originally published February 1, 2022 and most recently updated July 19, 2022.

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Normal Thyroid Hormone Levels – Endocrine Surgery

What is thyroid hormone?

Thyroid hormone is made by the thyroid gland, a butterfly-shaped endocrine gland normally located in the lower front of the neck. Thyroid hormone is released into the blood where it is carried to all the tissues in the body. It helps the body use energy, stay warm and keeps the brain, heart, muscles, and other organs working as they should.

Thyroid hormone exists in two main forms: thyroxine (T4) and triiodothyronine (T3). T4 is the primary form of thyroid hormone circulating in the blood (about 95%). To exert its effects, T4 is converted to T3 by the removal of an iodine atom; this occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. T3 normally accounts for about 5% of thyroid hormone circulating in the blood.

Most thyroid hormone in the blood is bound by protein, while only a small fraction is “free” to enter tissues and have a biologic effect. Thyroid tests may measure total (protein bound and free) or free hormone levels.

Production of thyroid hormone by the thyroid gland is controlled by the pituitary, another endocrine gland in the brain. The pituitary releases Thyroid Stimulating Hormone (abbreviated TSH) into the blood to stimulate the thyroid to make more thyroid hormone. The amount of TSH that the pituitary sends into the bloodstream depends on the amount of thyroid hormone in the body. Like a thermostat, if the pituitary senses low thyroid hormone, then it produces more TSH to tell the thyroid gland to produce more. Once the T4 in the bloodstream goes above a certain level, the pituitary’s production of TSH is shut off. In this way, the pituitary senses and controls thyroid gland production of thyroid hormone. Endocrinologists use a combination of thyroid hormone and TSH testing to understand thyroid hormone levels in the body.

What is a TSH test?

Thyroid tests
Blood tests to measure low or high TSH levels are readily available and widely used. Not all thyroid tests are useful in all situations.

TSH Test
The best way to initially test thyroid function is to measure the TSH (Thyroid Stimulating Hormone) level in a blood sample. Changes in TSH can serve as an “early warning system” — often occurring before the actual level of thyroid hormones in the body becomes too high or too low.

A high TSH level indicates that the thyroid gland is not making enough thyroid hormone (primary hypothyroidism). On the other hand, a low TSH level usually indicates that the thyroid is producing too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (central hypothyroidism). In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.

What is a T4 test?

T4 Tests
A Total T4 test measures the bound and free thyroxine (T4) hormone in the blood. A Free T4 measures what is not bound and able to freely enter and affect the body tissues.

What does it mean if T4 levels are abnormal?
Importantly, Total T4 levels are affected by medications and medical conditions that change thyroid hormone binding proteins. Estrogen, oral contraceptive pills, pregnancy, liver disease, and hepatitis C virus infection are common causes of increased thyroid hormone binding proteins and will result in a high Total T4. Testosterone or androgens and anabolic steroids are common causes of decreased thyroid hormone binding proteins and will result in a low Total T4.

In some circumstances, like pregnancy, a person may have normal thyroid function but Total T4 levels outside of the normal reference range. Tests measuring free T4 – either a free T4 (FT4) or free T4 index (FTI) – may more accurately reflect how the thyroid gland is functioning in these circumstances. An endocrinologist can determine when thyroid disease is present in the context of abnormal thyroid binding proteins.

What is a T3 test?

T3 Tests
T3 tests measure triiodothyronine (T3) levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity.

In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves’ disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 (active form) resulting in a lower proportion of T3.

T3 levels fall late during hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.

Measurement of Free T3 is possible but is often not reliable and therefore may not be helpful.

What is a normal thyroid (hormone) level?

To assess thyroid hormone status for low or high TSH levels we use TSH and FT4 tests. The normal value for a laboratory test is determined by measuring the hormone in a large population of healthy individuals and finding the normal reference range. Normal ranges for thyroid tests may vary slightly among different laboratories, and typical ranges for common tests are given below.

TSH normal values are 0.5 to 5.0 mIU/L. Pregnancy, a history of thyroid cancer, history of pituitary gland disease, and older age are some situations when TSH is optimally maintained in a different range as guided by an endocrinologist.

FT4 normal values are 0.7 to 1.9ng/dL. Individuals taking medications that modify thyroid hormone metabolism and those with a history of thyroid cancer or pituitary disease may be optimally managed with a different normal FT4 range.

Total T4 and Total T3 levels measure bound and free thyroid hormone in the blood. These levels are influenced by many factors that affect protein levels in the body, including medications, sex hormones, and liver disease.
A normal Total T4 level in adults ranges from 5.0 to 12.0μg/dL.
A normal Total T3 level in adults ranges from 80-220 ng/dL.

Free T3 assays are often unreliable and not routinely used to assess thyroid function.

What does it mean if my thyroid levels are abnormal?

Patterns of thyroid tests associated with thyroid disease

Primary Hypothyroidism
A high TSH and low thyroid hormone level (e. g. low FT4) can indicate primary hypothyroidism. Primary hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. Symptoms of hypothyroidism can include feeling cold, constipation, weight gain, slowed thinking, and decreased energy.
Causes of primary hypothyroidism include:

• Autoimmune thyroid disease, including Hashimoto’s thyroiditis
• Thyroid gland dysfunction due to a medication (e.g. amiodarone, tyrosine kinase inhibitors, or cancer immunotherapy)
• Removal of all or part of the thyroid gland
• Radiation injury to the thyroid (e.g. external beam radiation, radioactive iodine ablation treatment)
• Excess treatment with anti-thyroid medications (e.g. methimazole, propylthiouracil)

Early or mild hypothyroidism may present as a persistently high TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.

It is important to remember that normal TSH levels in older individuals (ages 70 and above) are higher than the normal ranges for younger individuals.

Primary Hyperthyroidism
A low TSH and a high thyroid hormone level (e.g. high FT4) can indicate primary hyperthyroidism. Primary hyperthyroidism occurs when the thyroid gland makes or releases too much thyroid hormone. Symptoms of hyperthyroidism can include tremors, palpitations, restlessness, feeling too warm, frequent bowel movements, disrupted sleep, and unintentional weight loss.
Causes of primary hyperthyroidism include:

• Graves’ disease
• Toxic or autonomously functioning thyroid nodule
• Multinodular goiter
• Thyroid inflammation (called thyroiditis) early in the course of disease
• Thyroid gland dysfunction due to a medication (e.g. amiodarone or cancer immunotherapy)
• Excess thyroid hormone therapy

Early or mild hyperthyroidism may present as a persistently low TSH and a normal FT4 hormone level. This pattern is called subclinical hyperthyroidism and your doctor may recommend treatment. Over time, untreated subclinical hyperthyroidism can worsen osteoporosis and contribute to abnormal heart rhythms.

Thyroiditis
Thyroid inflammation, also called thyroiditis, causes injury to the thyroid gland and release of thyroid hormone. Individuals with thyroiditis usually have a brief period of hyperthyroidism (low TSH and high FT4 or Total T4) followed by development of hypothyroidism (high TSH and low FT4 or Total T4) or resolution.

Some forms of thyroiditis are transient, like post-partum thyroiditis or thyroiditis following an infection, and often resolve on their own without need for medication.

Other forms of thyroiditis, like thyroiditis resulting from cancer immunotherapy, interferon alpha, or tyrosine kinase inhibitors, usually result in permanent hypothyroidism and require long term treatment with thyroid hormone replacement.

Your endocrinologist will monitor your thyroid tests during thyroiditis and can help determine if you need short- and long-term medications to balance your thyroid function and control any symptoms.

Central Hypothyroidism
A low TSH and a low FT4 may indicate pituitary disease. Detection of central hypothyroidism should prompt your doctor to check for problems in other pituitary hormones, an underlying cause, and you may need imaging tests to look at the pituitary gland.

Central hypothyroidism is treated with thyroid hormone replacement. Importantly, adequacy of thyroid replacement in central hyperthyroidism is assessed with FT4 and Total T4 tests not TSH as in primary hyperthyroidism, and deficiency in stress hormone cortisol should be assessed before starting thyroid treatment to prevent an adrenal crisis. 

Causes of central hypothyroidism include pituitary gland disease, such as a pituitary mass or tumor, history of pituitary surgery or radiation, pituitary inflammation (called hypophysitis) resulting from autoimmune disease or cancer immunotherapy, and infiltrative diseases.

Rare causes of abnormal thyroid function
Thyroid hormone resistance
Iodine induced hyperthyroidism
TSH-secreting tumor (TSH-oma)
Germ cell tumors
Trophoblastic disease
Infiltrative diseases, such as systemic scleroderma, hemochromatosis, or amyloidosis.

When abnormal thyroid function tests are not due to thyroid disease

While blood tests to measure thyroid hormones and thyroid stimulating hormone (TSH) are widely available, it is important to remember that not all tests are useful in all circumstances and many factors including medications, supplements, and non-thyroid medical conditions can affect thyroid test results. An endocrinologist can help you make sense of thyroid test results when there is a discrepancy between your results and how you feel. A good first step is often to repeat the test and ensure there are no medications that might interfere with the test results. Below are some common reasons for mismatch between thyroid tests and thyroid disease.

Non-thyroidal illness
Significant illness, such as an infection, cancer, heart failure, or kidney disease, or recent recovery from an illness can cause transient changes in the TSH. Fasting or starvation can also cause a low TSH. An endocrinologist can help to interpret changes in thyroid function tests in these circumstances to distinguish non-thyroid illness from true thyroid dysfunction.

Test interference
Biotin, a common supplement for hair and nail growth, interferes with many thyroid function tests and can lead to inaccurate results. Endocrinologists recommend stopping biotin supplements for 3 days before having a blood test for thyroid function.

Individuals who have exposure to mice, like laboratory researchers and veterinarians, may develop antibodies against mouse proteins in their blood. These antibodies cross react with reagents in multiple thyroid function tests and cause unpredictable results. A specialized assay can accurately measure thyroid hormone levels and TSH in this circumstance.

I don’t feel well, but my thyroid tests are normal

Thyroid blood tests are generally accurate and reliable. If you do not have low or high TSH levels and your thyroid tests are normal, your symptoms may not be related to thyroid disease, and you may want to seek additional evaluation with your primary care physician.

How is hypothyroidism treated?

What is thyroid medication?

Thyroid Hormone Treatment
Levothyroxine is the standard of care in thyroid hormone replacement therapy and treatment of hypothyroidism. Levothyroxine (also called LT4) is equivalent to the T4 form of naturally occurring thyroid hormone and is available in generic and brand name forms.

How do I take levothyroxine?
To optimize absorption of your thyroid medication, it should be taken with water at a regular time each day. Multiple medications and supplements decrease absorption of thyroid hormone and should be taken 3–4 hours apart, including calcium and iron supplements, proton pump inhibitors, soy, and multivitamins with minerals. Because of the way levothyroxine is metabolized by the body, your doctor may ask you to take an extra pill or skip a pill on some days of the week. This helps us to fine tune your medication dose for your body and should be guided by an endocrinologist.

For patients with celiac disease (autoimmune disease against gluten) or gluten sensitivity, a gluten free formulation of levothyroxine is available. Some individuals may have genetic variant that affects how the body converts T4 to T3 and these individuals may benefit from the addition of a small dose of triiodothyronine.

Liothyronine is replacement T3 (triiodothyronine) thyroid hormone. This medication has a short half-life and is taken twice per day or in combination with levothyroxine. Liothyronine alone is not used for treatment of hypothyroidism long term.

Other formulations of thyroid hormone replacement include natural or desiccated thyroid hormone extracts from animal sources. Natural or desiccated thyroid extract preparations have greater variability in the dose of thyroid hormone between batches and imbalanced ratios if T4 vs T3. Natural or animal sources of thyroid hormone typically contain 75% T4 and 25% T3, compared to the normal human balance of 95% T4 and 5% T3. Treatment with a correct balance of T4 and T3 is important to replicate normal thyroid function and prevent adverse effects of excess T3, including osteoporosis, heart problems, and mood and sleep disturbance. An endocrinologist can evaluate symptoms and thyroid tests to help balance thyroid hormone medications.

How do I know if my thyroid dose is correct?

Monitoring thyroid levels on medication
Correct dosing of thyroid hormone is usually assessed using the same tests for diagnosis of thyroid disease, including TSH and FT4. Thyroid tests are typically checked every 4-6 weeks initially and then every 6 to 12 months once stable. In special circumstances, such as pregnancy, a history of thyroid cancer, central hypothyroidism, amiodarone therapy, or use of combination T4 and T3 thyroid hormone replacement, your endocrinologist may check different thyroid tests. Additionally, your endocrinologist will evaluate for symptoms of hyperthyroidism and hypothyroidism and perform a physical exam.

Women who are pregnant and women who may become pregnant should only be treated with levothyroxine (T4). Only T4 efficiently crosses the placenta to provide thyroid hormone to the developing fetus. Thyroid hormone is critical in early pregnancy for brain development. Normal ranges for thyroid tests in pregnancy are different and change by trimester. Women with thyroid disease in pregnancy or who are considering pregnancy should be under the care of an endocrinologist to guide therapy.

Individuals with a history of thyroid cancer, even if only a portion of the thyroid was removed, also have different target ranges for TSH and FT4 tests. Thyroid hormone replacement in these individuals is closely tied to ongoing thyroid cancer surveillance, monitoring of thyroid cancer tumor markers, and dynamic assessment of recurrence risk. These patients are optimally managed by a multidisciplinary team including an endocrinologist and endocrine surgeon.

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Standards for the level of thysotropic hormone in the blood: the current state of the problem | Samsonova

One of the most controversial issues in modern thyroidology is the issue of TSH blood levels [4, 10]. The interest in this problem is understandable, since it is well known that the determination of the concentration of TSH in the blood is considered today as a reference test in the laboratory assessment of the functional state of the thyroid gland, which allows timely detection of any violation of its function, including at the stage of asymptomatic hyper- and hypothyroxinemia. Thus, an increase in the content of TSH in the blood is the earliest laboratory sign of not only obvious, but also threatened thyroid pathology, especially thyroid insufficiency. In this regard, it is quite obvious that the verification of thyroid insufficiency largely depends on the standard upper limit of the TSH level in the blood. Currently, it is generally accepted that the concentration of TSH in the blood more than 4-5 mU / l indicates a decrease in thyroid function.

This article is a continuation of the discussion on the standards of the upper limit of normal for the level of TSH in the blood, open on the pages of both foreign and domestic journals.

The reason for the discussion was the latest recommendations of the US National Academy of Clinical Biochemistry to reduce the upper limit of normal for the level of TSH in the blood from 4 to 2.5 mU/l [8]. The basis for making such decisions was the results of the epidemiological study NHANES-111, which showed that during the examination of 13,344 people receiving adequate iodine prophylaxis, the level of TSH in the blood above 2.5 mU/l was determined in no more than 5% of cases [11] . At the same time, the study did not include those population groups that could potentially have deviations in the functional state of the thyroid gland [11]. Similar results were obtained in the European study SHIP-1 [18]. Thus, as a result of a survey of 1488 adults in Pomerania, no more than 5% had a TSH level in the blood above 2.12 mU/l [18].

It should be noted that not only after the publication of the recommendations of the US National Academy of Clinical Biochemistry, but also long before that, articles began to appear in foreign literature indicating that adult patients with a TSH level in the blood of 2–4 mU/l, according to a number of clinical signs and laboratory tests differ from the population with TSH levels in the blood below 2 mU/l. So, back in 1992, J. Staub et al. showed that a group of adults with an average TSH content in the blood of 3.0 ± 0.3 mU/l demonstrates a hyperergic TSH response to thyroliberin stimulation, which, as is known, indicates a decrease in the functional reserve of the thyroid gland [16]. According to the data of the Wickham study, in the group of people with a TSH level in the blood above 2 mU/l, overt hypothyroidism is more often diagnosed in the future [17]. Finally, in adults, this level of TSH is associated with an increased risk of hypercholesterolemia [7, 9, 14], endothelial dysfunction [12], and miscarriage [15]. According to our data, such a concentration of TSH in the blood of women of reproductive age is associated with hypoestrogenemia. Thus, every 8th (12.5%) woman of reproductive age, who, when assessing the functional state of the thyroid gland, determined the level of TSH in the blood from 2 to 4 mU / l, had a reduced level of estrogen in the blood (median estradiol in this group of women was 167 pmol/l), while all women with TSH blood levels below 2 mU/l had estradiol levels within the normal range (median estradiol 235.25 pmol/l; /> = 0.01) [5] .

Moreover, in pregnant women (the most vulnerable part of the population in terms of the formation of pathological conditions associated with hypothyroxinemia), the level of TSH in the first trimester of gestation of more than 2 mU/l is currently recognized as an increased risk factor for the development of gestational hypothyroxinemia. So, according to our data, gestational hypothyroxinemia occurs in almost every 2nd pregnant woman with diffuse endemic goiter, who has a TSH level of 2 to 4 mU/l in the first trimester of gestation (/> = 0.05) [2].

Thus, a similar blood TSH level in adults is associated with a known spectrum of pathological conditions, which today are a recognized consequence of chronic hypothyroxinemia.

At the same time, it should be emphasized that all the accumulated knowledge and understanding of the clinical and prognostic significance of the concentration of TSH in the blood more than 2, but less than 4 mU/l was obtained on the basis of a survey of the adult population. The following data allow us to form an opinion on the significance, legitimacy and expediency of isolating this particular range of TSH levels in the blood and in pediatric practice. Thus, according to the results of a study by D.E. Shilin (2002), children and adolescents (l = 114) with a basal TSH level in the blood above 2 mU/l (average 2. 57 ± 0.06 mU/l) , differ from children and adolescents (l = 475) with a basal TSH level below 2 mU/l (average 1.19± 0.02 mU/l) [6].

In 94.1% of children (p < 0.05) of this group, a hyperergic TSH response to thyroliberin stimulation is observed, which indicates a reduced functional reserve of the thyroid gland [6]. According to the same author, such children and adolescents have significantly (/> = 0.03) higher concentrations of atherogenic lipid fractions, and adolescent girls with a similar level of TSH in the blood show signs of age-related immaturity of the uterus and gonads (p = 0.01) [6]. In addition, such girls are prone to polymenorrhea (menstruation lasts an average of 5.5 ± 0.3 days versus 4.7 ± 0.1 days in the group of girls with TSH levels in the blood below 2 mU/l; p = 0.01) and a lower level of estradiol in the blood (mean estradiol content 162 ± 23 pmol/l versus 239 ± 22 pmol/l in the group of girls with a TSH concentration in the blood of less than 2 mU/l; p = 0. 05) [6].

According to our data, it is adolescent girls with TSH levels in the blood above 2 but below 4 mU/l that are most vulnerable in terms of the formation of functional disorders of the reproductive system. So, according to the results of our research, every 2nd (54%) girl with a similar level of TSH in the blood has menstrual dysfunction of the type of opsomenorrhea (while only 28% of girls with a TSH level below 2 mU/l, Р = 0.032) [1].

So, in our opinion, today there are enough arguments in favor of the fact that the level of TSH in the blood from 2 to 4 mU/l in children also reflects the earliest in terms of onset and the mildest in severity thyroid insufficiency.

Obviously, thyroid insufficiency in iodine-deficient regions has its own evolution. In our opinion, the evolution of thyroid insufficiency can be represented as follows: 1) a normal level of free thyroxin and a TSH level of 2 to 4 mU/l, there are no clinical signs of hypothyroidism; 2) normal level of free thyroxine and TSH level above 4-5 mU/l, there are no clinical symptoms of hypothyroidism; 3) a reduced level of free thyroxine and a TSH level above 4-5 mU/l in combination with clinical signs of hypothyroidism. The last two stages of thyroid insufficiency are well known and are classified as subclinical and overt hypothyroidism, respectively.

At the same time, today there is no single generally accepted term that characterizes the level of TSH from 2 to 4 mU/l. This is understandable, since terminology issues are always the most difficult. In the English literature, the level of TSH in the traditionally normal range, but above 2 mU/l, is denoted by the following terms: “high-normal TSH” [14], “very mild thyroid failure” [15], “a lessened thyroid reserve” [15], “mildest form of subclinical hypothyroidism” [16]. We propose to use the term “minimal thyroid insufficiency” to designate the condition, which is reflected in the level of TSH from 2 to 4 mU/l. In our opinion, it is he who most accurately characterizes the earliest in terms of onset and the mildest in severity thyroid insufficiency.

At the same time, at a given level of TSH, the functionality of the thyroid gland should be assessed depending on its size. So, in persons without goiter, a slight increase in the level of TSH (2-4 mU / l) only indicates that, with normal sizes, the thyroid gland is not able to provide adequate production of thyroid hormones. In this group of people, a similar level of TSH reflects the readiness to turn on compensatory mechanisms leading to an increase in the size of the thyroid gland and to the normalization of the level of thyroid hormones. Thus, in persons with normal thyroid gland sizes, this condition cannot yet be classified as a pathology, but should be considered as a borderline condition.

In patients with long-term goiter, this level of TSH indicates that the increase in the size of the thyroid gland did not lead to the elimination of hypothyroxinemia and, therefore, the required level of thyroid hormones was not achieved. Most likely, in this case, there was a decrease in the compensatory and functional reserves of the thyroid gland due to a mild genetic defect in morpho- or hormonogenesis. Even with mild congenital insufficiency of the thyroid gland in conditions of insufficient iodine intake, the formation of goiter will not lead to the normalization of thyroid status, i.e., to the elimination of hypothyroxinemia and, consequently, the risk of iodine deficiency diseases.

We are deeply convinced that the use of the term “minimal thyroid insufficiency” in the context in which it is presented in the article will not only not mislead readers, but, on the contrary, will help to understand the essence of the problem and present the evolution of thyroid insufficiency in iodine-deficient regions.

It should be noted that another, no less, and perhaps more important issue of this discussion is whether people with a TSH blood level of 2 to 4 mU / l need therapy. Foreign and domestic authors consider the danger of expanding indications for verification of hypothyroidism and treatment of such a patient with levothyroxine preparations as a serious argument against the recognition of new standards for THG in the blood [4, 10].

In our opinion, the TSH level in the range from 2 to 4 mU/l only indicates that in the region of iodine deficiency the thyroid gland is able to maintain an ideal euthyroid state only if there is an adequate supply of iodine. It is quite obvious that in the absence of adequate iodine prophylaxis in regions with even moderate and / or mild iodine deficiency (i.e., in most of the territory of Russia), it is this degree of thyroid insufficiency that will continue to occur frequently and determine the formation of medically and socially significant iodine deficiency states. . Hence the conclusion that the vast majority of people living in these conditions and having a similar level of TSH in the blood need only adequate iodine prophylaxis. Adequate iodine prophylaxis in most of them is able to maintain an ideal euthyroid state for many years of life.

The exception is 2 groups of people. First of all, these are pregnant women with a TSH level in the first trimester of gestation above 2 mU/l, i. e., those with a risk factor for the development of gestational hypothyroxinemia [2]. Taking into account the exceptional role of the normal level of maternal thyroxine for the formation and maturation of the central nervous system of the unborn child and the need for rapid and effective correction of gestational hypothyroxinemia, today no one doubts and objects that pregnant women with a similar level of TSH need treatment with levothyroxine preparations. In addition, it is required to prescribe levothyroxine preparations to persons exposed to other (except for iodine deficiency) strimogenic environmental factors or having more pronounced genetically determined defects in morpho- or hormone genesis of the thyroid gland. It should be emphasized that these are extremely rare cases.

When deciding on the TSH level standards, the modern double standards used to assess the functional state of the thyroid gland in untreated individuals and in patients receiving levothyroxine replacement therapy are somewhat surprising [3, 13]. In this regard, another strong argument in favor of narrowing the normal range for the level of TSH in the blood is that the vast majority of researchers have recognized and do not raise objections to TSH levels ranging from 0.5 to 2 mU / l as reflecting the euthyroid state of the thyroid gland. in patients receiving replacement therapy with levothyroxine preparations [3, 13].

So, the above data convince us that today there are more than enough arguments in favor of recognizing the fact that (in both adults and children) the TSH level from 2 to 4 mU/l reflects the earliest in terms of appearance and the mildest thyroid insufficiency, namely minimal thyroid insufficiency.

Narrowing the range of normal levels of TSH in the blood from 0.5 to 2-2.5 mU / l and the speedy implementation of these standards in healthcare practice is a necessary condition for optimizing the early diagnosis, prevention, treatment of hypothyroxinemia and, consequently, the elimination of iodine deficiency conditions in Russia.

1. Bukanova SV Thyroid status and functional state of the reproductive system in children and adolescents living in an industrial metropolis with moderate to mild iodine deficiency: Authors. dis…. cand. honey. Sciences. -M., 2004.

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Thyroid stimulating hormone (TSH)

Thyroid stimulating hormone (TSH) is the main regulator of thyroid function, synthesized by the pituitary gland, a small gland located on the lower surface of the brain. Its main function is to maintain a constant concentration of thyroid hormones – thyroid hormones that regulate the processes of energy production in the body. When their blood levels decrease, the hypothalamus releases a hormone that stimulates the secretion of TSH by the pituitary gland.

Russian synonyms

Thyroid stimulating hormone, thyrotropin, TTU.

Synonyms English

Thyroid-stimulating Hormone (THS), Thyrotropin.

Research method

Electrochemiluminescent immunoassay.

Detection range: 0.005 – 1000 µIU/ml.

Units

µIU/mL (microinternational unit per milliliter).

What biomaterial can be used for research?

Venous blood.

How to properly prepare for an examination?

• Children under 1 year of age do not eat for 30-40 minutes before the test.
• Do not eat for 2-3 hours before the study, you can drink clean still water.
• Exclude (in agreement with the doctor) taking thyroid hormones, iodine preparations within 72 hours before the study.
• Eliminate (in agreement with the doctor) the use of steroid hormones within 48 hours before the study.
• Avoid physical and emotional overexertion within 24 hours prior to the study.
• Do not smoke for 3 hours prior to the study.

Study Overview

Thyroid stimulating hormone (TSH) is produced by the pituitary gland, a small gland located on the lower surface of the brain behind the sinus cavity. It regulates the production of thyroid hormones (thyroxine and triiodothyronine) according to the “feedback system”, which allows you to maintain a stable concentration of these hormones in the blood. With a decrease in the concentration of thyroid hormones, the secretion of thyroid-stimulating hormone increases and their production by the thyroid gland is stimulated, and vice versa – with an increase in the concentration of thyroxine and triiodothyronine, the secretion of thyroid-stimulating hormone decreases. Thyroid hormones are the main regulators of energy consumption in the body, and maintaining their concentration at the required level is extremely important for the normal functioning of almost all organs and systems.

Pituitary dysfunction can cause an increase or decrease in thyroid-stimulating hormone levels. With an increase in its concentration, thyroid hormones are released into the blood in abnormal amounts, causing hyperthyroidism. With a decrease in the concentration of thyroid-stimulating hormone, the production of thyroid hormones also decreases and symptoms of hypothyroidism develop.

The causes of impaired production of thyroid-stimulating hormone may be diseases of the hypothalamus, which begins to produce increased or decreased amounts of thyreoliberin, a regulator of TSH secretion by the pituitary gland. Diseases of the thyroid gland, accompanied by a violation of the secretion of thyroid hormones, can indirectly (by a feedback mechanism) affect the secretion of thyroid-stimulating hormone, causing a decrease or increase in its concentration in the blood. Thus, the study of TSH is one of the most important tests for hormones.

What is research used for?

• To determine the state of the thyroid gland, an indirect assessment of the production of thyroid hormones.
• To monitor the therapy of thyroid diseases.
• For the diagnosis of thyroid dysfunction in newborns.
• For diagnosing female infertility and monitoring its treatment.

When is the test ordered?

1. With an enlarged thyroid gland, as well as with symptoms of hyper- and hypothyroidism.
   • Symptoms of hyperthyroidism:
     • palpitations,
     • increased anxiety,
     • weight loss,
     • insomnia,
     • hand shake,
     • weakness, fatigue,
     • diarrhea,
     • intolerance to bright light,
     • decreased visual acuity,
     • puffiness around the eyes, their dryness, hyperemia, bulging.
   • Symptoms of hypothyroidism:
     • dry skin,
     • constipation,
     • cold intolerance,
     • edema,
     • hair loss,
     • weakness, fatigue,
     • menstrual disorders in women.

• Testing may be ordered at regular intervals to monitor the effectiveness of thyroid therapy. TSH levels are often assessed in newborns at risk for thyroid disease.

What do the results mean?

Reference values ​​

Causes of increased thyroid-stimulating hormone levels:

• hypothyroidism (primary and secondary),
• pituitary tumor (thyrotropinoma, basophilic adenoma),
• Hashimoto’s thyroiditis,
• syndrome of unregulated secretion of TSH,
• thyrotropin-secreting tumors of the lung,
• adrenal insufficiency,
• preeclampsia,
• lead poisoning,
• mental illness.

Causes of a decrease in the concentration of thyroid-stimulating hormone:

• diffuse toxic goiter,
• TSH-independent thyrotoxicosis,
• thyrotoxic adenoma (Plummer’s disease),
• hyperthyroidism of pregnancy,
• autoimmune thyroiditis with manifestations of thyrotoxicosis,
• mental illness,
• cachexia.

High and low levels of thyroid-stimulating hormone indicate thyroid dysfunction, but it is often impossible to determine the exact cause from TSH levels alone. Usually, for this, the level of thyroxine (T4) and triiodothyronine (T3) is additionally determined.

Important Notes

• The following drugs may increase thyroid-stimulating hormone levels: phenytoin, atenolol, clomiphene, motilium, metoprolol, valproic acid, propranolol, amiodarone, calcitonin, prednisolone, morphine, phenothiazine derivatives, benserazide, aminoglutethimide, metoclopramide, furosemide, iodides, lovastatin, methimazole, difenin, rifampicin.