Understanding TSH Levels

Thyroid-stimulating hormone (TSH) is a type of hormone that tells your thyroid how much thyroid hormone it should make. Your thyroid hormones are important for a number of functions, like regulating weight management, body temperature, and muscle strength.

A TSH test measures the amount of TSH in your blood. By measuring TSH levels, you can find out if your thyroid is making the right level of thyroid hormones. If your TSH levels are too high or too low, that might mean that the hormone is stimulating your thyroid too much or not enough, potentially pointing to a condition that needs addressing.

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What Is TSH?

The pituitary gland, a pea-sized gland in our brain, releases TSH. TSH helps regulate the amount of thyroid hormones the thyroid releases. As the name of the hormone suggests, TSH stimulates the thyroid gland, causing the thyroid gland to release thyroid hormones.

The thyroid gland is a butterfly-shaped gland that is located in the front of the neck and controls metabolism and other body functions.

The pituitary and thyroid glands work together to maintain the level of thyroid hormones in your blood. As the pituitary releases more TSH, more thyroid hormones get released. TSH levels may increase or decrease in different health conditions. In some cases, the TSH levels rise before the symptoms of the disease even appear.

What Is a TSH Test?

A TSH test measures the level of TSH in your blood. Knowing how much TSH is in your blood can reveal whether your thyroid is working properly. A healthcare provider will perform a TSH test by drawing blood from a vein in your arm. That blood sample is then sent to a laboratory, where levels of TSH in the blood are measured.

Your healthcare provider might recommend a TSH test if you have any symptoms of high or low thyroid levels. A TSH test serves as the first-line screening test in people with suspected thyroid problems.

You might need regular TSH tests if you:

  • Take thyroid hormone medication because it’s already been determined that you’re not making enough thyroid hormones 
  • Have had your thyroid removed
  • Have been treated for having high levels of thyroid hormones

A TSH test might also be used in part of the diagnosis of any suspicious growth on your thyroid.

Generally, there are no special preparations you need to take before the test. If you are having other blood tests at the same time, you may need to fast for those. Check with your healthcare provider for guidance.

TSH Levels

Normal TSH ranges depend on several factors, including a person's age, sex, and race. For instance, because older adults usually have higher levels of TSH, their normal range is considered higher.

There is some debate over the normal values of TSH. Normal ranges for TSH have generally been considered to be between 0.35-4.50 milli-international units per milliliter (mUI/mL). But it’s been argued that a healthy range is actually between 0.5-2.50 mIU/ml.

Anything below or above these normal ranges usually signals that your thyroid is making too much or too little thyroid hormone.

Low TSH Levels

TSH levels fall when there is an excess amount of thyroid hormones in your blood, a condition known as hyperthyroidism. When the thyroid hormone levels are higher than normal, the pituitary gland releases less TSH so that the thyroid gland doesn’t get stimulated. This prevents the release of even more thyroid hormones.

Hyperthyroidism is also known as overactive thyroid. Hyperthyroidism increases the activity of a lot of bodily processes, which can lead to symptoms like excessive sweating, increased appetite, and diarrhea.

Low levels of TSH will only reveal that you might have hyperthyroidism; they won’t be able to tell what is causing the problem. Further tests are needed to determine the cause. But some of the most common conditions that cause hyperthyroidism—and that a low TSH level might be a sign of—include:

  • Graves’ disease: This autoimmune disorder that attacks the thyroid is the most common cause. 
  • Toxic multinodular goiter: This condition, which involves an enlarged thyroid gland, is the most common cause among older people. 
  • Inflammation of the thyroid (thyroiditis): This can be due to medication or a viral infection and can also happen after pregnancy.

TSH levels may also be a little lower in the first three months of pregnancy. Further testing can confirm whether the drop-off was just temporary or a sign of a condition.

High TSH Levels

TSH levels rise when your thyroid gland is not producing enough thyroid hormone. When there is a low amount of thyroid hormone in the blood—a condition known as hypothyroidism—the pituitary gland releases large quantities of TSH to stimulate the thyroid gland so that more thyroid hormone is produced.

Hypothyroidism is also known as underactive thyroid. Hypothyroidism decreases the activity of a lot of bodily processes, leading to symptoms like weight gain, fatigue, and poorer concentration.

High levels of TSH can point to hypothyroidism, but they won't reveal the cause of the problem. Further tests are needed to determine the cause. Some conditions that might cause high levels of TSH include:

  • Hashimoto's disease (This autoimmune disorder that attacks the thyroid is the most common cause of hypothyroidism.)
  • Inflammation of the thyroid (thyroiditis)
  • Radiation therapy to the thyroid
  • Thyroid surgery

People over 80 might have higher TSH levels even without the presence of any thyroid condition.

Treatment for Abnormal TSH Levels

If you have abnormal levels of TSH, your healthcare provider will likely order more blood tests to determine what is causing your hyperthyroidism (low TSH) or hypothyroidism (high TSH). Once the cause is determined, you can receive proper treatment for the overproduction or underproduction of thyroid hormone. Getting thyroid production under control will help bring TSH levels back to normal.

Treatment for Low TSH

Low levels of TSH means that there is an excess amount of thyroid hormone in your blood. Increased levels of thyroid hormone cause complications in the long term, so hyperthyroidism treatment focuses on lowering the hormone levels. The approach on how to do this mainly depends on the underlying cause of the overproduction of thyroid hormones.

Antithyroid medications work by decreasing the amount of hormones your thyroid produces.

If Graves’ disease is causing low TSH, a popular treatment is radioactive iodine therapy. In this therapy, radioactive iodine is used to destroy the overactive thyroid tissue cells. For most patients, a single dose of radioactive iodine is enough to control hyperthyroidism.

Surgery to remove the thyroid gland is a treatment option for severe cases of hyperthyroidism.

If your thyroid is destroyed with the radioactive iodine or removed, you will need to forever take thyroid hormone replacement pills.

Before any treatment may be able to normalize your hormone levels, your healthcare provider might prescribe medication to manage your symptoms. This can include a beta-blocker, a medication that can help manage symptoms like sweating and fast heart rate.

Treatment for High TSH

High TSH in the blood means that there are low levels of thyroid hormone in your blood. The treatment of hypothyroidism mainly involves hormone replacement therapy. In hormone replacement therapy, thyroid hormone is given in the form of pills or injections. The hormone replacement keeps the thyroid hormone at normal levels to relieve the symptoms of hypothyroidism.

The healthcare provider usually recommends taking a pill daily before breakfast or three hours after dinner. Hormone injections are given if someone is unable to take the medicine by mouth.

You will need to have follow-up blood tests to see how the therapy is working and gauge whether the dose needs to be adjusted. Once the correct dose is found, you will need to have regular blood work to keep an eye on your hormone levels.

A Quick Review

TSH is a hormone that your brain’s pituitary gland releases. TSH stimulates the thyroid gland to release its thyroid hormone, which controls the body's functions and metabolism. A TSH test measures the amount of TSH in your blood. When TSH levels rise above or fall below the normal range, it could indicate a thyroid condition that is causing an abnormal level of thyroid hormone in the blood. These conditions are called hyperthyroidism and hypothyroidism and can be treated. Abnormal TSH levels may or may not require treatment depending on the cause and the severity of the symptoms. Talk to a healthcare provider about your TSH test and other tests that might be required based on your symptoms. 

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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