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Tests & Procedures : Lab Tests

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Thyroid Stimulating Hormone

Does this test have other names?

TSH,  thyrotropin test

What is this test?

This is a blood test that measures your level of thyroid stimulating hormone (TSH). Health care providers use this test to diagnose problems affecting the thyroid.

Your thyroid is a butterfly-shaped gland located near the base of your throat above your collarbones. The thyroid makes two hormones, T3 and T4, that affect your energy levels, mood, weight, and other important parts of your health.

The pituitary gland in your brain makes a chemical called TSH, which triggers your thyroid to make T3 and T4. When your pituitary gland produces too much or too little TSH, this can cause your thyroid to be overactive (hyperthyroidism) or underactive (hypothyroidism). 

Why do I need this test?

You may need this test if you have symptoms of thyroid problems.

Symptoms of hyperthyroidism include:

  • Anxiety

  • Irritability

  • Weakness in the arms and legs

  • Insomnia

  • Hand tremors

  • Sweating

  • Low tolerance for heat

  • Irregular heartbeat

  • Fatigue

  • Unexplained weight loss

  • More frequent bowel movements than usual

  • Eye irritation or bulging eyes, which are symptoms of Graves' disease, a common cause of hyperthyroidism

  • Menstrual irregularity

  • Enlarged breasts and erectile dysfunction in men

Symptoms of hypothyroidism include:

  • Fatigue

  • Low tolerance for cold

  • Weight gain

  • Hair loss

  • Eye swelling

  • Slower heart rate

  • Shortness of breath

  • Constipation

  • Menstrual irregularity

  • Loss of consciousness, although this is rare

Health care providers may also check TSH levels when diagnosing depression and dementia. 

What other tests might I have along with this test?

In addition to T4, you may have other tests of thyroid-related substances, including:

  • T4

  • Free T4

  • T3

  • Free T3

  • Thyroglobulin, which helps produce and store thyroid hormones

  • TSH receptor-stimulator antibodies, which is used to diagnose Graves' disease

  • Thyroid antiperoxidase antibodies and thyroglobulin antibodies, which are used to diagnose a condition called Hashimoto's thyroiditis

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

The normal range for TSH varies by lab, but the usual range is 2 to 11 microunits per milliliter (mU/mL).

Low TSH may mean you have hyperthyroidism, and high TSH can mean hypothyroidism. The results of other thyroid tests can help to determine the cause. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Some medications keep the pituitary gland from releasing TSH. These include:

  • Phenothiazines

  • Phenytoin

  • Dopamine

  • Glucocorticoids

Other drugs that can affect thyroid tests include:

  • Beta blockers

  • Dexamethasone

  • Enoxaparin

  • Furosemide

  • Heparin

  • NSAIDs

  • Salicylates

How do I get ready for this test?

Tell your doctor if you're taking medication. Certain medications can affect thyroid test results.

Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.