Hyperthyroidism can develop if your thyroid is overactive. A TSH test is one way to find out whether your thyroid gland is functioning normally. A low TSH level can be an early sign of thyroid disease.

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Thyroid-stimulating hormone (TSH) is a chemical that your pituitary gland makes. TSH works by activating your thyroid gland to release additional hormones to regulate your metabolism.

Hyperthyroidism can develop when your thyroid is too active and overproduces these metabolic hormones.

In this article, you will learn what a normal range for TSH is and what kind of results to expect from a TSH test if you have hyperthyroidism.

Learn more about hyperthyroidism.

Healthcare professionals can measure your TSH with a TSH blood test. Since TSH instructs your thyroid on how much of each thyroid hormone (T3, T4, free T3, and reverse T3) to make, results outside the typical range can serve as early signs of a thyroid disorder.

TSH levels are measured by analyzing hormone levels in a blood sample. A healthcare professional will usually take this blood sample from a vein in your arm or hand. The test does not usually require any special preparations or fasting beforehand.

The normal range for TSH is 0.4–5.5 milli-international units per liter (mIU/L). While you might assume that a higher-than-normal TSH level means you have hyperthyroidism, that’s not always the case.

Hyperthyroidism indicates an overactive thyroid, which produces too much thyroid hormone. A doctor will usually diagnose it if your TSH level falls below 0.4 mIU/L.

TSH levels below the normal range are classified as hyperthyroidism, meaning your thyroid may be overactive. Numbers above that range are classified as hypothyroidism and could signal an underactive thyroid.

In hypothyroidism, your thyroid does not make enough thyroid hormones. A lower-than-average TSH level can also indicate hypothyroidism if your pituitary gland isn’t functioning properly.

Hyperthyroidism can be treated with medications or therapies to try to reduce the activity of your thyroid or suppress its hormone production. Some medications that might be used to treat hyperthyroidism are:

Radioiodine medications work by destroying thyroid cells to reduce hormone production. A healthcare professional will check your thyroid hormone levels after starting treatment to determine when you may need more or less medication or other treatments.

In some cases, surgery might be necessary to remove part or all of your thyroid.

TSH tests can signal a problem with the chemical that tells your thyroid how much of each thyroid hormone to make. Sometimes TSH levels can be used to identify a problem before your thyroid hormones move too far out of balance. However, TSH levels won’t provide any information about what is causing your thyroid dysfunction.

In rare cases, an abnormal TSH level can also be a sign of a problem with your pituitary gland.

Additional tests that healthcare professionals might perform if you have a TSH level that’s too high or too low include:

Where is TSH produced?

TSH is produced in your pituitary gland, a tiny gland near the base of your brain, just behind your nose.

Where is the thyroid gland?

The thyroid is a butterfly-shaped gland in your neck. It wraps around the front of your trachea (windpipe) just below your voice box.

What kinds of things do thyroid hormones control?

Thyroid hormones control metabolic functions and may affect your:

  • weight
  • energy levels
  • body temperature
  • hair, skin, and nail growth
  • calcium regulation

Your TSH levels indicate whether your thyroid gland is working properly. A low TSH level can be an early sign of a hyperactive thyroid gland and hyperthyroidism.

Even after you start treatment, a healthcare professional may check your TSH levels to find out how well your medications are working and when it might be time for surgery.