What is a TSH test?

TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. The thyroid is a small, butterfly-shaped gland located near your throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. TSH is made in a gland in the brain called the pituitary. When thyroid levels in your body are low, the pituitary gland makes more TSH. When thyroid levels are high, the pituitary gland makes less TSH. TSH levels that are too high or too low can indicate your thyroid isn’t working correctly.

Other names: thyrotropin test

What is it used for?

A TSH test is used to find out how well the thyroid is working.

Why do I need a TSH test?

You may need a TSH test if you have symptoms of too much thyroid hormone in your blood (hyperthyroidism), or too little thyroid hormone (hypothyroidism).

Symptoms of hyperthyroidism, also known as overactive thyroid, include:

• Anxiety
• Weight loss
• Tremors in the hands
• Increased heart rate
• Puffiness
• Bulging of the eyes
• Difficulty sleeping

Symptoms of hypothyroidism, also known as underactive thyroid, include:

• Weight gain
• Tiredness
• Hair loss
• Low tolerance for cold temperatures
• Irregular menstrual periods
• Constipation

What happens during a TSH test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don’t need any special preparations for a TSH blood test. If your health care provider has ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

High TSH levels can mean your thyroid is not making enough thyroid hormones, a condition called hypothyroidism. Low TSH levels can mean your thyroid is making too much of the hormones, a condition called hyperthyroidism. A TSH test does not explain why TSH levels are too high or too low. If your test results are abnormal, your health care provider will probably order additional tests to determine the cause of your thyroid problem. These tests may include:

• T4 thyroid hormone tests
• T3 thyroid hormone tests
• Tests to diagnose Graves’ disease, an autoimmune disease that causes hyperthyroidism
• Tests to diagnose Hashimoto’s thyroiditis, an autoimmune disease that causes hypothyroidism

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a TSH test?

Thyroid changes can happen during pregnancy. These changes are usually not significant, but some women can develop thyroid disease during pregnancy. Hyperthyroidism occurs in about one in every 500 pregnancies, while hypothyroidism occurs in approximately one in every 250 pregnancies. Hyperthyroidism, and less often, hypothyroidism, may remain after pregnancy. If you develop a thyroid condition during pregnancy, your health care provider will monitor your condition after your baby is born. If you have a history of thyroid disease, be sure to talk with your health care provider if you are pregnant or are thinking of becoming pregnant.