What is the thyroid-stimulating hormone (TSH) test?

This blood test measures how well your thyroid gland is working. This gland, which is located at the lower front of the neck, may be normal, underactive, or overactive. The thyroid gland is critical for maintaining many body functions, such as body temperature, heart rate, appetite, digestion, and maintaining your energy level.

Your pituitary gland is located at the base of your brain. It is about the size of a pea. It is the main gland of the body and controls the activity of your thyroid gland by producing thyroid-stimulating hormone (TSH).

• When your thyroid gland is underactive, your body produces more TSH to stimulate the gland and increase its activity.
• When your thyroid gland is overactive, your body decreases the amount of TSH to slow production of thyroid hormone.

Why is this test done?

The TSH test is used to:

• Check for thyroid disease
• Monitor thyroid hormone medicine levels
• Look for thyroid disease in newborns
• Diagnose female infertility problems

How do I prepare for this test?

You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Don’t stop any of your regular medicines without first talking to your healthcare provider about it.

How is it done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

A higher than normal TSH level usually means there is not enough thyroid hormone in your blood. This condition is called hypothyroidism. You may have hypothyroidism because:

• Your thyroid gland is damaged.
• Your thyroid gland is not working normally.
• Your thyroid gland is infected or inflamed.
• Your thyroid gland was removed or destroyed and you are not taking enough replacement thyroid hormone.
• Rarely you can have a high TSH level and have too much thyroid hormone. This only happens when there is a benign tumor in the pituitary gland that is producing too much TSH and making your thyroid gland produce too much thyroid hormone.

A lower than normal TSH level may mean that your thyroid gland is making too much thyroid hormone (hyperthyroidism) or you are taking too much replacement thyroid hormone. This may be because:

• Your thyroid gland was removed or destroyed.
• Your thyroid gland is infected or inflamed.
• Your thyroid gland has grown too large.
• Your thyroid has a tumor that is making extra thyroid hormone.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

• If you need more tests
• What kind of treatment you may need
• What lifestyle, diet, or other changes you might need to make