TSH (Thyroid-stimulating hormone) Test

TSH stands for thyroid stimulating hormone. Another name for it is thyrotropin. A TSH test is a blood test that measures this hormone.

A TSH level that is too high or too low may be a sign of a thyroid problem. The thyroid is a small, butterfly-shaped gland in the front of your neck. Your thyroid makes hormones that control how your body uses energy.

Thyroid hormones affect nearly every organ and control many of your body's most important functions. For example, they affect your breathing, heart rate, weight, digestion, and even your mood. If you don't have enough thyroid hormones in your blood, many of your body functions will slow down.

But if you have too much, many body functions will speed up. Your thyroid is controlled by a gland in your brain called the pituitary gland. The pituitary gland makes thyroid-stimulating hormone (TSH).

TSH tells your thyroid how much thyroid hormone it needs to make. If the thyroid hormone level in your blood is too low, your pituitary gland makes larger amounts of TSH to tell your thyroid to work harder. If your thyroid hormone level is too high, the pituitary gland makes little or no TSH.

By measuring the TSH level in your blood, you can find out if your thyroid is making the right level of hormones.

Why this test is done

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

Hyperthyroidism is also called overactive thyroid. Having more thyroid hormones than you need speeds up your body functions and causes symptoms that can vary from person to person. The symptoms may include::

• Weight loss, even though you may be eating more than usual
• Rapid or irregular heartbeat
• Feeling nervous or irritable
• Trouble sleeping
• Fatigue
• Shaky hands, muscle weakness
• Sweating or being very sensitive to heat
• Frequent bowel movements (pooping a lot) or diarrhea
• Goiter (enlarged thyroid that may cause your neck to look swollen)

Adults over age 60 may have different symptoms than younger adults. For example, they may lose their appetite or withdraw from other people. Sometimes, this can be mistaken for depression or dementia.

Hypothyroidism (too little thyroid hormone) is also called underactive thyroid. Not having enough thyroid hormone slows down your body functions and causes symptoms that can vary from person to person. The symptoms may include:

• Fatigue
• Weight gain
• Being very sensitive to cold
• Joint and muscle pain
• Dry skin
• Dry, thinning hair
• Heavy or irregular menstrual periods
• Fertility problems in women
• Depression
• Constipation

Because hypothyroidism develops slowly, many people don't notice symptoms of the disease for months or even years.

You may also have a TSH test and other tests to help diagnose unusual bumps or lumps on your thyroid. The tests will help your health care provider check for thyroid cancer or thyroid nodules (growths on your thyroid that aren't cancer).

How to prepare

You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to. 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 provider will let you know if there are any special instructions.

Sample type

Blood

Other names for this test

thyrotropin test, thyrotropic hormone