Thyroid-stimulating hormone (TSH) is released by the pituitary gland in the brain. TSH stimulates the thyroid gland in your neck to make thyroid hormones.

A thyroid-stimulating hormone (TSH) test is a blood test that screens for the level of TSH in your body. Low levels or high levels of TSH can signal a thyroid disorder.

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Why is a thyroid-stimulating hormone test important?

The thyroid produces three primary hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. These hormones regulate metabolism, growth and other bodily functions. The thyroid needs TSH to make these hormones.

If you’re experiencing signs and symptoms of a thyroid disorder, a TSH test can determine how well the thyroid is working. There are two different kinds of thyroid disorders: hypothyroidism and hyperthyroidism.

What is hypothyroidism, and what are its symptoms?

When the thyroid doesn’t produce enough hormones, it is called hypothyroidism. This condition can cause metabolism to slow down.

The signs of hypothyroidism include fatigue, weakness, difficulty concentrating, unexplained weight gain, constipation, dry skin, hair loss and cold sensitivity. It can also cause menstrual period irregularity in women.

The most common causes of hypothyroidism are:

  • Hashimoto’s disease, an autoimmune disease that causes the body to attack its own thyroid cells
  • Thyroiditis, an inflammation of the thyroid gland that is caused by a viral infection or autoimmune disorder. This condition affects the production of thyroid hormones.
  • Postpartum thyroiditis, a temporary form of thyroiditis that develops in some women after childbirth
  • Iodine deficiency, an extremely rare condition in the United States

What is hyperthyroidism, and what are its symptoms?

When the thyroid produces too many hormones, it is called hyperthyroidism. This condition can cause metabolism to speed up.

The signs of hyperthyroidism include unexpected weight loss, excessive hunger, anxiety, irritability and difficulty sleeping. It can also cause increased heart rate and dryness, bulging or puffiness around the eyes.

The most common causes of hyperthyroidism are:

  • Graves’ disease, a disorder that causes the thyroid to enlarge and make too many hormones
  • Thyroiditis, an inflammation of the thyroid gland that causes the thyroid to make too many hormones and release them all at once. It eventually leads to hypothyroidism.
  • Too much iodine in the body. This can happen if medications containing iodine, such as cough syrups or medicines to treat heart arrhythmias, are overused.
  • Thyroid nodules

What should you expect with a thyroid-stimulating blood test?

A healthcare provider will draw blood, which will go to a lab for testing. Above-normal levels usually indicate an underactive thyroid.

Below-normal levels usually indicate an overactive thyroid. Ask your healthcare provider to explain your specific results.

If you have symptoms of a thyroid disorder, talk to a healthcare provider about a thyroid-stimulating hormone test.

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