What is a TSH blood test. How is the TSH test performed. What do TSH levels indicate about thyroid function. When should you get a TSH test. How to interpret TSH test results. What factors can affect TSH levels. How is TSH related to other thyroid hormones.

The Basics of TSH and Thyroid Function

Thyroid-stimulating hormone (TSH) plays a crucial role in regulating the body’s metabolism and overall thyroid function. Produced by the pituitary gland, TSH acts as a messenger, prompting the thyroid gland to produce and release thyroid hormones into the bloodstream. These hormones, primarily thyroxine (T4) and triiodothyronine (T3), are responsible for controlling the body’s metabolic rate, energy production, and various other essential functions.

The relationship between TSH and thyroid hormones operates on a feedback loop. When thyroid hormone levels in the blood are low, the pituitary gland increases TSH production to stimulate the thyroid gland. Conversely, when thyroid hormone levels are high, TSH production decreases. This delicate balance helps maintain optimal thyroid function and metabolic homeostasis.

The Importance of TSH in Thyroid Health

TSH serves as a sensitive indicator of thyroid function, making it an invaluable tool for diagnosing and monitoring thyroid disorders. By measuring TSH levels, healthcare providers can gain insights into the thyroid gland’s activity and identify potential issues before they manifest as more severe symptoms.

• Elevated TSH levels often indicate an underactive thyroid (hypothyroidism)
• Low TSH levels may suggest an overactive thyroid (hyperthyroidism)
• Normal TSH levels typically indicate proper thyroid function

The TSH Blood Test: Purpose and Procedure

A TSH blood test measures the amount of thyroid-stimulating hormone in your blood. This simple yet effective diagnostic tool helps healthcare providers assess thyroid function and identify potential thyroid disorders. The test is often performed as part of a routine health screening or when thyroid dysfunction is suspected.

When is a TSH Test Recommended?

Healthcare providers may order a TSH test in various scenarios:

• As part of a routine health check-up, especially for individuals over 35
• When symptoms of thyroid dysfunction are present
• To monitor the effectiveness of thyroid treatment
• During pregnancy or when planning to conceive
• For individuals with a family history of thyroid disorders

The TSH Test Procedure

The TSH test is a straightforward blood test that requires no special preparation. During the procedure:

1. A healthcare professional will clean the area, usually the inside of your elbow or back of your hand
2. A needle is inserted into a vein to draw a small amount of blood
3. The blood sample is collected in a vial or tube
4. The needle is removed, and the puncture site is covered with a bandage
5. The blood sample is sent to a laboratory for analysis

While some individuals may experience slight discomfort or bruising at the puncture site, these effects are typically minor and short-lived.

Interpreting TSH Test Results

Understanding TSH test results is crucial for assessing thyroid health. Normal TSH levels typically range from 0.5 to 5 microunits per milliliter (µU/mL). However, it’s important to note that reference ranges may vary slightly between laboratories and that individual factors can influence what’s considered “normal” for a particular person.

TSH Levels and Thyroid Function

TSH levels can indicate various thyroid conditions:

• High TSH (above 5 µU/mL): May indicate hypothyroidism
• Low TSH (below 0.5 µU/mL): May suggest hyperthyroidism
• Normal TSH (0.5-5 µU/mL): Generally indicates proper thyroid function

It’s important to remember that TSH levels can fluctuate throughout the day, with levels typically being highest in the early morning. For this reason, healthcare providers often recommend having the test performed early in the day for the most accurate results.

Factors Affecting TSH Levels

Several factors can influence TSH levels, potentially affecting test results. Understanding these factors is essential for accurate interpretation and diagnosis.

Medications and Supplements

Certain medications and supplements can impact TSH levels:

• Amiodarone (heart medication)
• Dopamine (used to treat various conditions)
• Lithium (used in bipolar disorder treatment)
• Potassium iodide (used for thyroid protection)
• Prednisone and other glucocorticoids
• Biotin (vitamin B7) supplements

If you’re taking any of these substances, it’s crucial to inform your healthcare provider before undergoing a TSH test. They may recommend temporarily discontinuing certain medications or supplements to ensure accurate results.

Other Influencing Factors

Additional factors that can affect TSH levels include:

• Age (TSH levels may naturally increase with age)
• Pregnancy (TSH levels can fluctuate during pregnancy)
• Stress (acute stress can temporarily alter TSH levels)
• Time of day (TSH levels are typically highest in the morning)
• Certain medical conditions (e.g., pituitary disorders)

TSH and Other Thyroid Function Tests

While the TSH test is a valuable tool for assessing thyroid function, it’s often used in conjunction with other thyroid tests to provide a more comprehensive picture of thyroid health. These additional tests may include:

• Free T4 (FT4) test
• Free T3 (FT3) test
• Total T4 and T3 tests
• Thyroid antibody tests (e.g., anti-TPO)

By examining the results of multiple thyroid function tests, healthcare providers can more accurately diagnose thyroid disorders and develop appropriate treatment plans.

TSH Levels in Special Populations

Interpreting TSH levels can be more complex in certain populations, requiring special considerations and potentially different reference ranges.

Pregnancy and TSH

During pregnancy, TSH levels naturally fluctuate due to hormonal changes. The American Thyroid Association recommends the following trimester-specific TSH ranges for pregnant women:

• First trimester: 0.1-2.5 µU/mL
• Second trimester: 0.2-3.0 µU/mL
• Third trimester: 0.3-3.0 µU/mL

Proper thyroid function is crucial during pregnancy, as it plays a vital role in fetal development. Healthcare providers often monitor TSH levels closely in pregnant women to ensure optimal thyroid function.

TSH in Older Adults

As people age, TSH levels tend to increase naturally. Some laboratories use higher upper limits for TSH reference ranges in older adults, sometimes as high as 7 µU/mL. This adjustment helps prevent overdiagnosis of hypothyroidism in the elderly population.

Beyond TSH: The Bigger Picture of Thyroid Health

While TSH is a crucial marker of thyroid function, it’s essential to consider it as part of a broader approach to thyroid health. Maintaining optimal thyroid function involves various lifestyle factors and health practices.

Nutrition and Thyroid Health

A balanced diet rich in essential nutrients can support thyroid function. Key nutrients for thyroid health include:

• Iodine: Found in iodized salt, seaweed, and fish
• Selenium: Present in Brazil nuts, fish, and eggs
• Zinc: Found in oysters, beef, and pumpkin seeds
• Vitamin D: Obtained through sunlight exposure and fatty fish
• Iron: Found in red meat, spinach, and legumes

While these nutrients are important, it’s crucial to maintain a balanced intake and consult with a healthcare provider before starting any supplementation regimen.

Lifestyle Factors Affecting Thyroid Health

Several lifestyle factors can impact thyroid function and overall health:

• Stress management: Chronic stress can affect thyroid hormone production
• Exercise: Regular physical activity supports overall metabolic health
• Sleep: Adequate sleep is essential for hormone balance and thyroid function
• Environmental factors: Limiting exposure to endocrine disruptors may support thyroid health

By addressing these lifestyle factors alongside medical management, individuals can support their thyroid health and overall well-being.

The Future of Thyroid Testing and Management

As medical science advances, new approaches to thyroid testing and management are emerging. These developments may offer more personalized and comprehensive care for individuals with thyroid disorders.

Emerging Technologies in Thyroid Testing

Several innovative technologies are being explored to enhance thyroid diagnosis and monitoring:

• Genetic testing: Identifying genetic markers associated with thyroid disorders
• Artificial intelligence: Using machine learning to improve the interpretation of thyroid test results
• Continuous monitoring devices: Developing wearable technologies to track thyroid hormone levels in real-time
• Personalized reference ranges: Establishing individualized “normal” ranges based on a person’s unique physiology

These advancements may lead to more accurate diagnoses and tailored treatment plans in the future.

Integrative Approaches to Thyroid Health

There is growing interest in integrative approaches to thyroid health, combining conventional medical treatments with complementary therapies. Some areas of exploration include:

• Mind-body techniques: Incorporating practices like meditation and yoga to support thyroid function
• Herbal medicine: Investigating the potential of certain herbs to support thyroid health
• Functional medicine: Addressing underlying imbalances that may contribute to thyroid dysfunction
• Nutritional therapy: Developing personalized dietary plans to optimize thyroid function

While these approaches show promise, it’s essential to work with qualified healthcare providers and ensure that any complementary therapies are used in conjunction with, not in place of, conventional medical treatments.

Understanding TSH blood test results is crucial for maintaining optimal thyroid health. By recognizing the significance of TSH levels, considering influencing factors, and taking a holistic approach to thyroid care, individuals can work with their healthcare providers to achieve and maintain proper thyroid function. As research in this field continues to evolve, we can look forward to even more precise and personalized approaches to thyroid health management in the future.

TSH test Information | Mount Sinai

Thyrotropin; Thyroid stimulating hormone; Hypothyroidism – TSH; Hyperthyroidism – TSH; Goiter – TSH

A TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It prompts the thyroid gland to make and release thyroid hormones into the blood.

Endocrine glands release hormones (chemical messengers) into the bloodstream to be transported to various organs and tissues throughout the body. For instance, the pancreas secretes insulin, which allows the body to regulate levels of sugar in the blood. The thyroid gets instructions from the pituitary to secrete hormones which determine the rate of metabolism in the body (the more hormone in the bloodstream, the faster the chemical activity; the less hormone, the slower the activity).

The pituitary secretes thyroid stimulating hormone (TSH), which stimulates the thyroid gland to secrete hormones that affect body metabolism.

How the Test is Performed

A blood sample is needed. Other thyroid tests that may be done at the same time include:

• T3 test (free or total)
• T4 test (free or total)
• Anti-TPO (antibodies against thyroid peroxidase)

How to Prepare for the Test

There is no preparation needed for this test. Ask your health care provider about any medicines you are taking that may affect the test results. DO NOT stop taking any medicines without first asking your provider.

Medicines you may need to stop for a short time include:

• Amiodarone
• Dopamine
• Lithium
• Potassium iodide
• Prednisone or other glucocorticoid medicines

The vitamin biotin (B7) can affect the results of the TSH test. If you take biotin, talk to your provider before you have any thyroid function tests.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

Your provider will order this test if you have symptoms or signs of an overactive or underactive thyroid gland. It is also used to monitor treatment of these conditions.

Your provider may also check your TSH level if you are planning to get pregnant.

Normal Results

Normal values range from 0. 5 to 5 microunits per milliliter (µU/mL).

TSH values can vary during the day. It is best to have the test early in the morning. Experts do not fully agree on what the upper number should be when diagnosing thyroid disorders. Some labs will use a higher normal range limit for older people (even as high as 7 µU/mL).

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

If you are being treated for a thyroid disorder, your TSH level will likely be kept between 0.5 and 4.0 µU/mL, except when:

• A pituitary disorder is the cause of the thyroid problem. A low TSH may be expected.
• You have a history of certain types of thyroid cancer. A TSH value below the normal range may be best to prevent the thyroid cancer from coming back.
• A woman is pregnant. The normal range for TSH is different for women who are pregnant. Your provider may suggest that you take thyroid hormone, even if your TSH is in the normal range.

What Abnormal Results Mean

A higher-than-normal TSH level is most often due to an underactive thyroid gland (hypothyroidism). There are many causes of this problem.

A lower-than-normal level may be due to an overactive thyroid gland, which can be caused by:

• Graves disease
• Toxic nodular goiter or multinodular goiter
• Too much iodine in the body (due to receiving iodine contrast used during imaging tests, such as CT scan)
• Taking too much thyroid hormone medicine or prescribed natural or over-the-counter supplements that contain thyroid hormone

Use of certain medicines may also cause a lower-than-normal TSH level. These include glucocorticoids/steroids, dopamine, certain chemotherapy drugs, and opioid painkillers such as morphine.

Risks

There is little risk involved with having your blood taken.Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood buildup under the skin)
• Infection (a slight risk any time the skin is broken)

Guber HA, Oprea M, Rusell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 25.

Jonklaas J, Cooper DS. Thyroid. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 213.

Salvatore D, Cohen R, Kopp PA, Larsen PR. Thyroid pathophysiology and diagnostic evaluation. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 11.

Weiss RE, Refetoff S. Thyroid function testing. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 78.

Last reviewed on: 1/9/2022

Reviewed by: Robert Hurd, MD, Professor of Endocrinology and Health Care Ethics, Xavier University, Cincinnati, OH. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

Thyroid-Stimulating Hormone (TSH) Test – Testing.com

Test Quick Guide

Thyroid-stimulating hormone (TSH) signals the thyroid gland to make hormones that control how your body uses and stores energy, called metabolism. Testing the TSH level in your blood can reveal if your thyroid gland is functioning normally.

The TSH level is tightly controlled by the levels of other thyroid hormones in your blood. Hypothyroidism — high TSH levels — may indicate your thyroid is underactive and needs more stimulation. Low levels, or hyperthyroidism, may mean it’s overactive and needs less stimulation. About 5% of American adults have hypothyroidism, and slightly more than 1% have hyperthyroidism.

About the Test

Purpose of the test

Your TSH level provides information about whether your thyroid gland is functioning normally. TSH is often tested as part of a thyroid panel, along with tests of hormones produced by the thyroid gland. If TSH is tested and the result is abnormal, additional thyroid tests may be ordered.

TSH testing may be used for the following reasons:

• To diagnose an underactive or overactive thyroid gland
• To screen for thyroid disease before it causes symptoms, especially in newborns
• To evaluate a thyroid nodule, a lump on the thyroid gland
• To evaluate a goiter, which is an enlargement of the thyroid gland
• To monitor your response to treatment for hypothyroidism, hyperthyroidism, or another thyroid condition

What does the test measure?

The TSH test measures TSH, which prompts the thyroid to produce other hormones. A butterfly-shaped gland in your neck, the thyroid makes the hormones triiodothyronine (T3) and thyroxine (T4). These control your metabolism, or how your body uses and stores energy.

Although TSH acts upon the thyroid gland by binding to the TSH receptor, it is made in the pituitary gland, sometimes called “the master gland,” because it produces many hormones that control the functions of other glands.

The pituitary gland can sense when your T3 and T4 hormone levels are too low or too high. In response, it will produce more or less TSH to stimulate your thyroid gland to produce the right amount of hormones.

If your thyroid is underactive, you may have high levels of TSH as your pituitary gland tries to stimulate the thyroid to produce more T3 and T4. And if your thyroid is overactive, your TSH may be abnormally low because your pituitary gland stops making TSH when your thyroid hormone levels are too high.

When should I get this test?

TSH is often the first test doctors order when they suspect you have a thyroid disorder. Both hypothyroidism and hyperthyroidism are common disorders. It is important to have your TSH checked if you have symptoms of these thyroid disorders. If so, your doctor may order a TSH or a thyroid panel test.

Symptoms of hypothyroidism include:

• Fatigue
• Depression
• Weight gain
• Feeling cold
• Painful joints and muscles
• Dry skin
• Thin and/or dry hair
• Slow heart rate
• Constipation
• Irregular menstrual periods
• Fertility problems

Symptoms of hyperthyroidism include:

• Weight loss
• Irritability
• Anxiety
• Insomnia
• Difficulty tolerating heat
• Mood swings
• Rapid or irregular heartbeat
• Loose, frequent bowel movements

TSH is also used to evaluate you if you are suspected to have other thyroid disorders, such as goiter, thyroid nodule, thyroid cancer, Graves’ disease, or Hashimoto’s thyroiditis. These disorders can cause hypothyroidism or hyperthyroidism.

Screening — testing without symptoms — with TSH for hypothyroidism in adults is controversial. It is most beneficial when early detection and treatment of disease help you avoid subsequent medical problems. Some organizations, such as the American Association of Clinical Endocrinology, the American Thyroid Association, and the Endocrine Society, favor routine screening for thyroid problems in adults without symptoms.

Other experts prefer screening only adults who are at increased risk of thyroid disorders, such as if you have autoimmune disorders or a family history of thyroid disease. The United States Preventive Services Task Force does not recommend screening for adults who are not pregnant. This task force believes there is not enough evidence that early thyroid disease detection results in better patient outcomes.

Because thyroid disorders can complicate pregnancy, screening with a TSH test during pregnancy is recommended for some women. Pregnant women without symptoms of thyroid problems may be screened if they:

• Have a family history of thyroid disease
• Live in an area where iodine deficiency is common
• Are over 30 years old
• Have a history of miscarriage, premature birth, or infertility
• Are significantly obese (with a body mass index over 40)
• Other risk factors are present

Newborn infants are routinely screened for congenital hypothyroidism, meaning an underactive thyroid that is present at birth. When caught early, the effects of hypothyroidism in infants can be successfully treated.

Blood levels of TSH will also be tested periodically in people who are being treated with replacement thyroid hormones due to hypothyroidism or because they’ve had surgery or radiation to the thyroid gland. By monitoring TSH, doctors can adjust the medication dose if necessary. Testing TSH may also be used to monitor you after hyperthyroidism treatment.

Finding a TSH Test

How can I get a TSH test?

TSH testing is most often performed at the doctor’s office or another medical setting like a laboratory or hospital. These tests are normally prescribed by a doctor but may be available without a doctor’s orders.

Can I take the test at home?

Several commercially available test kits allow you to provide a sample for TSH testing at home. Some kits test only TSH, and others test TSH in combination with other thyroid hormones or additional hormones, such as cortisol and free testosterone.

These kits may be purchased online and include the materials you need to take a finger-prick blood sample and return it to the company for testing. Your test results will be reported to you via a secure online platform.

At-home testing is convenient and can help you participate in your health care. But at-home tests cannot replace working with a health care provider. Share your concerns with your doctor if you have symptoms or are concerned your thyroid is not functioning properly. If an at-home test detects an abnormal TSH level, your doctor will likely retest the TSH and follow up with additional testing if the second TSH test is also abnormal.

How much does the test cost?

The cost of a TSH test will vary depending upon factors such as where it is performed and whether or not you have insurance coverage. Insurance will usually cover the cost of TSH testing if your doctor orders it to diagnose or treat a medical condition. You can check with your doctor, the lab, or your insurance company to learn more about the cost and what, if any, out-of-pocket costs you may be responsible for.

Taking a TSH Test

TSH testing requires a blood sample, which is usually taken from your arm in a doctor’s office, health clinic, hospital, or lab. Your doctor may recommend testing in the morning for the most accurate TSH result.

Before the test

Typically, no special preparations are needed prior to having a TSH test. It is a good idea to talk to your doctor about your medications, as certain medications may affect your test results.

If you are taking biotin or Vitamin B7 supplements, they should be discontinued at least two days before the TSH test, as they can interfere with the accuracy of your test results.

Multivitamins that contain small amounts of biotin are unlikely to interfere with the test results.

During the test

A blood sample is usually taken from a vein in your arm. The person drawing your blood may tie a band around your upper arm and will clean the area where the needle will enter your skin. A needle with a sample tube attached to it will be inserted into your vein, and a small amount of blood will be drawn into the tube. You may feel a slight sting when the needle pierces your skin.

TSH testing in a newborn involves taking a few drops of blood from the baby’s heel.

The process of taking a blood sample usually takes less than three minutes.

After the test

You will be asked to apply gentle pressure to the site where the blood was removed with a piece of gauze or bandage. The health provider will apply a bandage to the extraction site.

A blood draw is a very low-risk procedure. You may have slight bruising at the site where the blood sample was taken.

TSH Test Results

Receiving test results

Your doctor may share your test results with you, or you may be able to access them through an online portal. TSH results are often available within a few business days.

Interpreting test results

Your test results will indicate a blood level of TSH and whether it falls above or below normal limits, also called the reference range. Results are often reported in milli-international units per liter (mIU/L).

Reference ranges will vary slightly depending upon the laboratory used for the test. Additionally, there is some controversy in the medical community about what the upper limit of a normal TSH value should be and how to manage if you only have slightly elevated TSH levels.

The American Board of Internal Medicine uses an adult TSH reference range of 0.5–4.0 mIU/L. However, because they vary by laboratory, it’s important to ask your doctor about the reference range for your test results.

Doctors may take many factors into account when evaluating your TSH, including:

• Age: TSH levels tend to be higher if you are over the age of 80. Most older patients with slightly higher than normal TSH levels do not have any associated health problems.
• Pregnancy: Pregnancy causes changes in thyroid hormones. It is common for TSH to be slightly lower than normal during the first trimester, then slowly rise.
• Severe illness: If you are very sick with diseases not related to the thyroid you may have a low TSH temporarily.
• Other thyroid tests: The results of other tests, such as free T4 and thyroid antibodies, may also influence how a doctor interprets a TSH test.

A TSH value above the normal range may indicate the thyroid is underactive. When the TSH is below normal, it can be because the thyroid gland is making too much thyroid hormone. An abnormal TSH level is occasionally due to the pituitary gland not functioning correctly.

If you are being monitored for treatment of a thyroid condition, your doctor can tell you the target range in your case.

When you review the results of your TSH test with your doctor, it could be helpful to ask specific questions, such as the following:

• Is my level of TSH within the normal range?
• Do my test results suggest that my thyroid is overactive or underactive?
• What additional tests will you be ordering, if any?

• Thyroid Panel
• T4 Test
• T3 Test
• Thyroid Antibodies

Resources

• American Thyroid Association: Patient Information
  Learn More
• National Library of Medicine: Thyroid Diseases
  Learn More
• Office on Women’s Health: Thyroid disease
  Learn More

Sources

A. D.A.M. Medical Encyclopedia. Neonatal Hypothyroidism. Updated April 14, 2021. Accessed December 6, 2022. https://medlineplus.gov/ency/article/001193.htm

A.D.A.M. Medical Encyclopedia. Newborn Screening Tests. Updated May 24, 2021. Accessed December 6, 2022. https://medlineplus.gov/ency/article/007257.htm

A.D.A.M. Medical Encyclopedia. Simple Goiter. Updated February 1, 2022. Accessed December 6, 2022. https://medlineplus.gov/ency/article/001178.htm

A.D.A.M. Medical Encyclopedia. Thyroid Nodule. Updated May 13, 2020. Accessed December 6, 2022. https://medlineplus.gov/ency/article/007265.htm

A.D.A.M. Medical Encyclopedia. TSH Test. Updated January 9, 2022. Accessed December 6, 2022. https://medlineplus.gov/ency/article/003684.htm

American Board of Internal Medicine. ABIM Laboratory Test Reference Ranges. Updated January 2022. Accessed December 6, 2022. https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf

American Thyroid Association. Thyroid Function Tests. Date unknown. Accessed December 6, 2022. https://www.thyroid.org/thyroid-function-tests/

Connelly K, LaFranchi S. Clinical Features and Detection of Congenital Hypothyroidism. In: Geffner ME. UpToDate. Updated August 26, 2022. Accessed December 6, 2022. https://www.uptodate.com/contents/clinical-features-and-detection-of-congenital-hypothyroidism

MedlinePlus: National Library of Medicine. TSH (Thyroid-Stimulating Hormone). Updated August 3, 2022. Accessed December 6, 2022. https://medlineplus.gov/lab-tests/tsh-thyroid-stimulating-hormone-test/

National Heart, Lung, and Blood Institute. Blood Tests. March 24, 2022. Accessed December 6, 2022. https://www.nhlbi.nih.gov/health-topics/blood-tests

National Institute of Diabetes and Digestive and Kidney Diseases. Hyperthyroidism (Overactive Thyroid). Updated August 2021. Accessed December 6, 2022. https://www.niddk.nih.gov/health-information/endocrine-diseases/hyperthyroidism

National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid). Updated March 2021. Accessed December 6, 2022. https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism

Natural Medicine Comprehensive Database. Biotin. Therapeutic Research Center. Updated August 19, 2021. Accessed December 6, 2022. https://medlineplus.gov/druginfo/natural/313.html

Orlander PR, Varghese JM, Naik S. Hypothyroidism. Medscape. In Griffing GT, ed. Updated May 25, 2022. Accessed December 6, 2022. https://emedicine.medscape.com/article/122393-overview

Ross DS. Diagnosis of Hyperthyroidism. In: Cooper DS, ed. UpToDate. Updated February 15, 2022. Accessed December 6, 2022. https://www.uptodate.com/contents/diagnosis-of-hyperthyroidism

Ross DS. Diagnostic Approach To and Treatment of Thyroid Nodules. In: Cooper DS, ed. UpToDate. Updated June 7, 2022. Accessed December 6, 2022. https://www.uptodate.com/contents/diagnostic-approach-to-and-treatment-of-thyroid-nodules

Ross DS. Disorders That Cause Hypothyroidism. In: Cooper DS, ed. UpToDate. Updated October 12, 2022. Accessed December 6, 2022. https://www.uptodate.com/contents/disorders-that-cause-hypothyroidism

Ross DS. Laboratory Assessment of Thyroid Function. In: Cooper DS, ed. UpToDate. Updated June 14, 2022. Accessed December 6, 2022. https://www.uptodate.com/contents/laboratory-assessment-of-thyroid-function

Ross DS. Patient Education: Hypothyroidism (Underactive Thyroid) (Beyond the Basics) In: Cooper DS, ed. UpToDate. Updated April 20, 2021. Accessed December 6, 2022. https://www.uptodate.com/contents/hypothyroidism-underactive-thyroid-beyond-the-basics

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How to assess the functional state of the thyroid gland and what to do in a situation where the tests are inadequate? | Melnichenko

Introduction

Thyroid gland (thyroid) diseases are widespread in the population, often their main symptoms resemble other diseases, and the main method for verifying gland function disorders is the laboratory determination of the level of thyroid-stimulating (TSH) and thyroid hormones (T ₄ and T ₃ ). The TSH level is the most sensitive marker of thyroid function and, in combination with other clinical and laboratory parameters, determines the further tactics of patient management.

Thyroid function tests are often easy to evaluate, but the following should be kept in mind to interpret the test results correctly.

• The regulation of the hypothalamic-pituitary-thyroid axis is based on the principle of logarithmic negative feedback. Hypothalamus cells synthesize thyrotropin-releasing hormone (TRH) into the pituitary portal system. TRH stimulates the production of TSH in pituitary cells. On the other hand, TSH secretion is under strict inhibitory control from the level of T ₃ and T ₄ in the blood. A decrease in the level of T ₃ and T ₄ (even within normal fluctuations) increases the synthesis of TSH, and vice versa, an increase in the level of T ₃ and T ₄ quickly reduces the concentration of TSH. In addition, T ₃ and T ₄ reduce the response of TSH to TRH. TSH has a direct effect on all stages of the biosynthesis of T ₄ and T ₃ , stimulates the absorption of iodine from the blood by the thyroid gland, increases the activity of thyroid peroxidase and enhances the synthesis of thyroglobulin [1].
• The biosynthesis of thyroid hormones is a complex multi-stage process controlled by various enzyme systems. Iodine plays a major role in the biosynthesis of thyroid hormones. In the form of an inorganic anion, it is absorbed from the gastrointestinal tract into the blood, with the help of a sodium-iodine symporter, it is captured by thyroid cells, where a monoiodotyrosine molecule is synthesized in a redox reaction catalyzed by thyroid peroxidase. Then a second iodine atom is attached to monoiodotyrosine. It turns out a molecule with two iodine atoms, which is called diiodotyrosine. When two diiodotyrosine molecules condense, T 9 is formed0005 4 . T ₃ is formed as a result of the combination of mono- and diiodotyrosine molecules. Iodtyrosines and thyronines accumulate in the thyroid gland as part of thyroglobulin, which serves as the basis for the synthesis of hormones T ₃ and T ₄ [1].

Interpretation of research results

Diseases of the thyroid gland associated with a violation of its function, are its hyperfunction (hyperthyroidism), insufficiency of function (hypothyroidism), which in turn are divided according to severity into subclinical and manifest.

• In a hormonal study, subclinical primary hypothyroidism corresponds to a high content of TSH with normal T ₄ , manifest primary hypothyroidism – hypersecretion of TSH and a reduced concentration of T ₄ [2].
• With overt hyperthyroidism, the TSH concentration should be low, the serum levels of f.T ₄ and f.T ₃ increased.
• When there is a decrease in the concentration of TSH without a simultaneous increase in the concentration of thyroid hormones in the blood, this condition is regarded as subclinical hyperthyroidism.

However, it is often possible to encounter the fact that when obtaining the results of the analysis for TSH and T ₄ /T ₃ there are difficulties with the interpretation of the indicators: the results of laboratory studies do not correspond to the clinical picture and / or the normal functioning of the pituitary-thyroid axis.

For example, in a small but significant group of observations, the following results may be determined: slightly increased TSH and increased T ₄ or reduced TSH and reduced T ₄ , especially in the absence of obvious clinical manifestations.

Why do these situations occur and what needs to be ruled out to make a correct diagnosis?

The time of blood sampling for TSH assessment in normal practice does not matter – but if necessary, evaluate more precisely the fact of suppression with appropriate therapy for thyroid cancer, or when evaluating indications for taking thyroxin in pregnant women, or when patients are worried about discrepancies in received different times of day of the data, it must be remembered that TSH (but not T ₄ ) there is a circadian rhythm. Due to the small value of the TSH itself, this rhythm is hardly noticeable, and both when it is increased by more than 10 mU / ml, and when it is suppressed to numbers below 0.1, it is insignificant.

Normally, TSH production is characterized by a circadian rhythm, with a decrease in TSH concentration during the day reaching 58%. The value of individual variability in TSH concentration over 4-6 weeks in persons without thyroid dysfunction does not exceed 43%. Therefore, the interpretation of TSH concentration values ​​requires taking into account the time of blood sampling, while in the daytime, both in normal conditions and in hypothyroidism (including patients already receiving replacement therapy), a physiological decrease in TSH content by 20–60% of the initial one occurs [3].

Factors affecting test results

When obtaining test results that do not fit into either the physiology of the hypothalamic-pituitary-thyroid axis or the clinical picture, it is always necessary to exclude errors in blood sampling and laboratory interference.

Test results may be affected by:

• determination of the “total” rather than “free” fraction of hormones (thyroxine-binding globulin, albumin, transthyretin and their high concentrations can lead to an increase in the content of the total fraction of T ₃ and T ₄ ) [4];
• circulating antibodies to T ₄ and T ₃ that can bind labels [5, 6];
• heterophile antibodies used in the analysis [7];
• the use of fractionated and unfractionated heparin (there is an increase in FT ₃ /T ₄ due to their displacement from the connection with transport proteins) [8];
• the phenomenon of macrothyrotropinemia (circulation of macroisoforms of TSH, in which a significantly increased TSH is determined without an increase in T ₄ and clinical manifestations) [9].

The use of a two-step analysis method (back titration) with a washing step prior to labeling reduces, but does not completely eliminate, the interferences described above [7]. In such a situation, it is necessary to re-determine TSH and T ₄ in a laboratory where more accurate methods are used (for example, the equilibrium dialysis method). In this regard, interaction with laboratory specialists is often key to understanding the situation in which inadequate results of tests of the functional state of the thyroid gland may occur [10].

History data play an important role in making a diagnosis, therefore, even before laboratory testing, the patient should be informed about all the medications he is taking. For example, estrogens, oral contraceptives increase the content of thyroxin-binding globulin, thereby increasing the content of total fractions T ₄ and T ₃ [4].

Deiodinase 1 activity and T9 conversion rate decrease in patients taking amiodarone0005 4 in T ₃ , there is an increase in the concentration of s. T ₄ with a normal content of TSH, and the concentration of s.

Propylthiouracil, glucocorticoids, propranolol and iodinated drugs and contrast agents may reduce the conversion of T ₄ to T ₃ through a mechanism similar to amiodarone [10]. The results of analyzes with a normal or elevated content of T ₄ with an increased content of TSH in a patient on replacement therapy with levothyroxine sodium indicate low compliance with this therapy (short-term and irregular intake of thyroid hormone preparations can lead to this situation, since the concentration of thyroid hormones varies greatly) [12]. Moreover, taking blood after taking levothyroxine sodium will result in an absorption test of the drug, but will not allow you to judge its concentration in the blood for most of the time.

It has been shown that taking sufficiently large doses of vitamin B ₇ (or biotin) distorts the results of many laboratory tests, including tests of the functional state of the thyroid gland [13]. That is, the patient needs to learn not only about the medications taken, but also about vitamins and dietary supplements.

Syndrome of euthyroid pathology, in which there is a reduced concentration of T ₃ and various fluctuations in the concentration of f.T ₄ and TSH, depending on the phase of the disease, is one of the reasons why there is no need for laboratory testing of thyroid hormones in the intensive care unit (with the exception of cases of suspected changes in thyroid function). In various acute or chronic non-thyroid diseases, abnormal indicators of thyroid function can be determined. These pathological conditions include starvation, protein-energy malnutrition, severe trauma, myocardial infarction, chronic renal failure, diabetic ketoacidosis, anorexia nervosa, cirrhosis of the liver, burn disease, and sepsis. Concentration T ₄ decreases as the disease worsens, the content of reverse T ₃ in serum increases (in clinical practice, there is no need to study this indicator, its determination is carried out for scientific purposes). At the same time, clinically ill patients are in a euthyroid state, and their TSH concentration does not increase until the onset of recovery, when it can increase for a short time [14]. However, it is worth remembering that the clinic of hypothyroidism is nonspecific and disguises itself as other (often neuropsychiatric) diseases, and even healthy people in 15% of cases have at least three symptoms of hypothyroidism [15].

Thyrotropinoma and resistance to thyroid hormones

Thus, after re-confirmation of a slightly elevated TSH level and a high concentration of T ₄ in another laboratory, the exclusion of drugs that could affect the result of research and severe somatic pathology (with the exception of complaints of increased pulse) requires further differential diagnosis between the following conditions: TSH-secreting pituitary adenoma and resistance to thyroid hormones.

If these diseases are suspected, it is important to determine further manipulations to establish a diagnosis due to the fact that these diseases are clinically similar, but the treatment differs significantly.

Obviously, if a pituitary tumor is suspected, the first step is to have an MRI or CT scan of the brain. However, in recent years, the detection of pituitary microadenomas – incidentalomas – has increased, which must be differentiated from hormonally active pituitary tumors [16, 17]. Individuals with long-term uncompensated hypothyroidism may develop hyperplasia of thyrotrophs that mimic adenomas [18].

Therefore, the first-line tests are those with thyreoliberin and octreotide.

When stimulated with thyrotropin-releasing hormone (serum TSH concentration is measured 15 and 30 minutes before intravenous administration of TRH at a dose of 200–500 μg and 15 and 30 minutes after intravenous administration of TRH), patients with thyrotropinoma have a reduced or absent TSH secretion response (increase in concentration less than 150%) after the test [17].

In patients with resistance to thyroid hormones, the response to TRH stimulation remains intact or increases [19]. This is due to the fact that in individuals with a pituitary tumor, TSH secretion remains autonomous even after TRH administration. In our country, this test has not been used in the last 20 years, since thyroliberin preparation turned out to be unnecessary for other purposes, although it was used a lot in the past (for example, in the diagnosis of euthyroid Graves’ disease or hyperprolactinemia syndromes) [20, 21].

In the test with octreotide (administration of 100 µg), the concentration of TSH, FL ₄ /T ₃ decreases in both diseases, but with long-term use of prolonged somatostatin analogue, the content of thyroid hormones remains stably reduced in thyrotropinoma [22].

In order to assess the severity of thyrotoxicosis, markers of peripheral effects of thyroid hormones can be assessed. Namely, the C-terminal telopeptide of type 1 collagen and sex steroid-binding globulin (SHBG). Also, the content of SSSH and the alpha subunit of glycoprotein pituitary hormones (alpha-SU) will be increased in thyrotropinoma [16, 23, 24]. However, such an increase needs to be interpreted due to the fact that the concentration of alpha-SU can be increased in menopausal women, and SHSH levels can be affected by synthetic estrogen therapy.

Thyroid hormone resistance syndrome is often a diagnosis of exclusion. For its final confirmation, a molecular genetic study is required.

The prevalence of this syndrome is 1:40,000–1:50,000 newborns, and it occurs with the same frequency in both sexes [25, 26].

Two genes encoding thyroid receptors, TRα and TRβ, have been identified and are located on chromosomes 17 and 3. The receptors have three main isoforms: TRα1 (primary expression: CNS, myocardium, skeletal muscle), TRβ1 (liver, kidneys) and TRβ2 (pituitary and hypothalamus). With resistance to thyroid hormones, heterozygous TRβ mutations are most often detected. In total, more than 120 different mutations in the gene 9 have been identified so far.0189 TRHB [27].

Clinical manifestations of this syndrome depend on the location and degree of mutation activity. Often, patients are in a euthyroid state or note tachycardia at rest. When this disease is detected in children, attention is paid to impaired attention, hyperactivity, and a delay in physical development is possible. In addition, thyrotropinoma in children is casuistically rare.

Treatment of thyrotropinoma consists of transnasal adenomectomy, drug treatment – in the appointment of somatostatin analogues [28]. With this therapy, the content of thyroid hormones is normalized in more than 90%. Also, in 40% of cases, tumor regression occurs. Patients receiving this therapy should undergo a dynamic examination to identify side effects (cholelithiasis, hyperglycemia) [29]. In case of contraindications or ineffectiveness of surgical and medical methods of treatment, radiotherapy or radiosurgery is used.

Treatment of thyroid hormone resistance syndrome consists of symptomatic treatment, often with beta-adrenergic blockers (to control tachycardia). Radical treatment for this disease (surgical or radioiodine therapy) is unacceptable. The seemingly promising use of the drug TRIAC (triiodothyroacetic acid) to normalize the content of TSH and thyroid hormones did not give obviously good results, and the drug is not registered in our country [30].

There are other rare conditions that cause inadequate tests of the functional state of the thyroid gland (normal concentration of TSH with low concentration of f.T ₄ and high concentration of f.T ₃ ). This is an X-linked defect in the MCT8 gene. Clinically, this disease manifests itself from early childhood with a delay in psychomotor development, impaired speech, swallowing. More than 100 families with this syndrome have been described [10].

Violation of deiodination processes caused by a decrease in the synthesis of deiodinases is a rare disease (only 8 families have been described). Mental retardation, dysmotility, and muscle weakness are clinically noted. Hormonal examination reveals a high concentration of St. T ₄ , low concentration of T ₃ with normal or slightly elevated TSH [31, 32].

Conclusion

Based on the above, we can say that the tests of the functional assessment of the thyroid gland are not always easy to interpret, however, in such cases, a thorough additional examination of the patient and differential diagnosis are necessary to determine the tactics of further management.

Additional information

Conflict of interest. The authors declare that there are no apparent or potential conflicts of interest associated with the publication of these recommendations, which must be reported.

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12. Morris JC. How do you approach the problem of TSH elevation in a patient on high-dose thyroid hormone replacement? Clinic Endocrinol. 2009;70(5):671-673. doi: 10.1111/j.1365-2265.2009.03536.x.

13. Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017;318(12):1150-1160. doi: 10.1001/jama.2017.13705.

14. Msdmanuals.com [Internet]. Hershman JM. Euthyroid Sick Syndrome [cited 2018 Jul 20]. Available from: https://www.msdmanuals.com/professional/endocrine-and-metabolic-disorders/thyroid-disorders/euthyroid-sick-syndrome.

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18. Gurnell M, Rajanayagam O, Barbar I, et al. Reversible pituitary enlargement in the syndrome of resistance to thyroid hormone. thyroid. 1998;8(8):679-682. doi: 10.1089/thy.1998.8.679.

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Tests for thyroid hormones in St. Petersburg

Danae clinics have full-fledged clinical diagnostic laboratories where they perform tests (including a general blood test), urgently and in a planned manner, in order to adequately and promptly establish a diagnosis and start treatment on time.

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• Cost of blood tests
• What indicators does the analysis determine?
• Indications for
• Preparation for procedure

A blood test for thyroid hormones is a comprehensive study that is usually prescribed by a gynecologist, endocrinologist or mammologist. The technique allows you to explore the active elements that are produced in the pituitary gland and thyroid gland. These substances – hormones – are responsible for the work of almost all body systems.

Cost of a blood test

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Doctor appointment

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You can undergo the procedure at any time in our clinic “Danae”. Having our own laboratory allows us to significantly reduce the time of research and improve the accuracy of the results. Depending on the results obtained, our doctors will be able to prescribe you further examination or treatment of the disease.

What indicators does the analysis determine?

The thyroid gland affects the entire body, especially the work of the cardiovascular, digestive, nervous, hematopoietic and reproductive systems. Therefore, any change in the production of hormones will adversely affect human health.

The study reveals the following indicators:

• Thyroglobulin (TG). The level of this element is a kind of marker for the diagnosis of various thyroid tumors.
• Thyroid stimulating hormone (TSH). It is produced in the pituitary gland and is responsible for the work of the entire organ as a whole.
• Triiodothyronine (T3). This prohormone affects the redox processes occurring in the body.
• Thyroxine (T4). Associated with protein metabolism and other metabolic processes.
• Free hormones T3 and T4. They affect metabolic processes, regulate the rate of tissue growth.
• Antibodies to TSH receptors. This is necessary to identify diseases characterized by thyrotoxicosis syndrome.
• Antibodies to thyroglobulin (AT-TG) and thyroperoxidase (AT-TPO). The indicator will be required for the diagnosis of autoimmune diseases.

Both a comprehensive study and the study of individual prohormones can be carried out. In this case, the price of an analysis for thyroid hormones depends on the number of parameters studied.

Indications for

Tests to determine the hormonal levels are prescribed by the specialists of our clinic in the following cases:

• Irregular heart rhythm.
• Baldness or hair loss.
• Severe muscle pain.
• Decrease or disappearance of libido.
• Sudden weight loss or gain.
• Frequent dizziness.
• Menstrual disorders.
• Infertility.
• Feeling constantly tired and weak.
• Anemia.

Also, a violation of the hormonal balance may indicate headaches, increased blood pressure, digestive disorders.

The study is also prescribed for iodine deficiency, postpartum thyroid dysfunction and other diseases that are accompanied by hypo- or hyperthyroidism.

Preparation for procedure

Before donating blood, our doctor will explain a number of rules to you. Like many other laboratory tests, it is better to take a hormone test on an empty stomach. Before diagnosis, it is necessary to complete the course of hormonal drugs and not take iodine-containing drugs. It is important to remember that you cannot donate both total and free hormones T3 and T4 at the same time.