Thyroid Stimulating Hormone (TSH) Levels: High, Low, and Normal Meaning

Thyroid Stimulating Hormone (TSH) Levels: High, Low, and Normal Meaning

  • A TSH test measures blood levels of the thyroid-stimulating hormone to diagnose a thyroid disorder.
  • Your doctor will order a TSH test if you have symptoms of thyroid disorders such as hair loss or fatigue.
  • High TSH levels could be a sign of hypothyroidism, while low TSH levels can signal hyperthyroidism.
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Thyroid disorders, which affect approximately 20 million Americanscan be diagnosed with a TSH test, which measures levels of so-called thyroid-stimulating hormone (TSH) in your blood.

TSH is a hormone produced in the pituitary gland of the brain that supports thyroid function, says Juan JaumeMD, endocrinologist and professor at Faculty of Medicine and Life Sciences of the University of Toledo.

Thyroid function is important because it helps control your metabolism as well as basic growth and development. So if you have a thyroid disorder, it can lead to all sorts of problems like weight gain, fatigue, hair loss and much more.

Here is an overview of how the TSH test works and how to interpret its results.

What is a TSH test?

A TSH test is designed to identify abnormal levels of TSH in your blood, which may indicate a thyroid disorder, says Aleem KanjiMD, endocrinologist with Ethos Endocrinologya private practice.

Typically, your doctor will order a TSH test if you have key symptoms symptoms of thyroid dysfunctionsuch as excessive hair loss or weight changes.

The test will involve a blood draw, usually first thing in the morning, and the results take around 24 hours.

Interpretation of TSH Levels

Generally, normal TSH levels are between 0.5 and 5.0 mIU/L. However, this may vary for pregnant women as TSH levels naturally change as the pregnancy progressessays James.

TSH levels below 0.5 mIU/L or above 5.0 mIU/L can indicate different types of thyroid disorders that often require additional testing to diagnose. Here is an overview of what abnormal TSH levels can mean.

High TSH levels

A high TSH level is above 5.0 mIU/L and may suggest an underactive thyroid, aka hypothyroidism.

“Significantly elevated TSH is not dangerous on its own,” says Kanji. “However, the significant elevation indicates a concerning or potentially dangerous thyroid disorder.”

If you have hypothyroidism, there are several things that can cause it, but the most common is an autoimmune disease known as Hashimoto’s disease.

To confirm hypothyroidism, a doctor will usually perform a follow-up test that measures your T4 levels, the main form of thyroid hormone circulating in the blood. A high TSH level and a low T4 level may indicate that you have an underactive thyroid.

Low levels of TSH

A low TSH is less than 0.5 mIU/L and usually occurs when thyroid hormone levels in the blood are too highKanji said.

This is because when the brain detects high levels of thyroid hormone, it produces less TSH to prevent the thyroid glands from producing more thyroid hormone.

Accordingly, a low TSH level suggests hyperthyroidism or an overactive thyroid. There can be a few different causes of hyperthyroidism, but one of the most common is an autoimmune disease known as Graves disease.

If your TSH levels are low, your doctor will likely order another test to assess your T4 or T3 levels — another type of thyroid hormone. A high T4 or T3 with a low TSH indicates hyperthyroidism, Kanji says.

How to Treat Thyroid Dysfunction

You cannot increase or decrease TSH levels on your own. Therefore, whether you have hypothyroidism or hyperthyroidism, treatment will likely require some form of medical help.

Treat hypothyroidism

Treatment options for hypothyroidism most often include drugs that restore proper hormonal levels.

“There’s nothing you can do on your own to lower your TSH levels,” Jaume says. “Thyroid autoimmune hypothyroidism requires thyroid hormone replacement.”

Treating Hyperthyroidism

If your doctor finds other markers of hyperthyroidism, they may suggest different treatment options, including:

  • Antithyroid drug
  • Beta-blockers
  • radioactive iodine
  • Surgery to remove the thyroid

Insider’s Takeaways

A TSH test is one of the first tests used to determine whether or not someone has a thyroid disorder. This test measures the levels of TSH produced by the pituitary gland in your brain.

A high TSH level could indicate hypothyroidism or an underactive thyroid, while a low TSH level could indicate hyperthyroidism or an overactive thyroid. If your TSH levels are abnormal, your doctor will likely order more tests to determine the root cause.