What is a TSH Test?
TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. TSH levels that are 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 in your body, including your heart. They help control your weight, body temperature, muscle strength, and even your mood. If you don’t have enough thyroid hormones in your blood, many of your body functions slow down. If you have too much, many body functions 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 levels in your blood are too low, your pituitary gland makes larger amounts of TSH to tell your thyroid to work harder. If your thyroid hormone levels are too high, the pituitary gland makes little or no TSH. By measuring TSH levels in your blood, you can find out if your thyroid is making the right level of hormones.
Other names: thyrotropin test
What is it used for?
A TSH test is used to find out how well your thyroid is working. It can tell if you have hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone) in your blood. But a TSH test can’t show what is causing a thyroid problem.
If you take prescription thyroid hormone medicine because of hypothyroidism or because you had your thyroid removed, you’ll have regular TSH tests to check your thyroid hormone levels. TSH tests are also used to monitor your thyroid hormone levels after treatment for hyperthyroidism.
Why do I need a TSH test?
You may need a TSH test if you have symptoms of too much or too little thyroid hormone in your blood.
Hyperthyroidism (too much thyroid hormone) is also called overactive thyroid. Having more thyroid hormones than you need speeds up your body functions and causes symptoms that 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)
- Goiter (enlarged thyroid)
Hypothyroidism (too little thyroid hormone) is also called underactive thyroid. Not having enough thyroid hormone slows down your body functions and causes symptoms that include:
- Fatigue
- Weight gain
- Being very sensitive to cold
- Joint and muscle pain
- Dry skin
- Dry, thinning hair
- Heavy or irregular menstrual periods
- Depression
- Constipation
You may also have a TSH test, along with other tests, to help diagnose unusual bumps or lumps on your thyroid that may be thyroid cancer or thyroid nodules (growths on your thyroid that aren’t cancer).
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 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?
Your TSH test results can tell you if your thyroid is making too much or too little thyroid. But the test can’t explain why your TSH levels may be too high or too low.
If your test results aren’t normal, your provider will probably order other thyroid blood teststo find out what’s causing your thyroid problem. These blood tests may include:
- T4 thyroid hormone test
- T3 thyroid hormone test
- Thyroid antibodies test to help diagnose an autoimmune thyroid disorder, such as:
- Graves’ disease, the most common cause of hyperthyroidism
- Hashimoto’s disease, that the most common cause of hypothyroidism
In certain cases, an abnormal TSH result may be a sign of a pituitary gland problem, but this doesn’t happen often.