About the Test
Purpose of the test
Your TSH level provides information about whether your thyroid gland is functioning normally. TSH is often tested as part of a thyroid panel, along with tests of hormones produced by the thyroid gland. If TSH is tested and the result is abnormal, additional thyroid tests may be ordered.
TSH testing may be used for the following reasons:
- To diagnose an underactive or overactive thyroid gland
- To screen for thyroid disease before it causes symptoms, especially in newborns
- To evaluate a thyroid nodule, a lump on the thyroid gland
- To evaluate a goiter, which is an enlargement of the thyroid gland
- To monitor your response to treatment for hypothyroidism, hyperthyroidism, or another thyroid condition
What does the test measure?
The TSH test measures TSH, which prompts the thyroid to produce other hormones. A butterfly-shaped gland in your neck, the thyroid makes the hormones triiodothyronine (T3) and thyroxine (T4). These control your metabolism, or how your body uses and stores energy.
Although TSH acts upon the thyroid gland by binding to the TSH receptor, it is made in the pituitary gland, sometimes called “the master gland,” because it produces many hormones that control the functions of other glands.
The pituitary gland can sense when your T3 and T4 hormone levels are too low or too high. In response, it will produce more or less TSH to stimulate your thyroid gland to produce the right amount of hormones.
If your thyroid is underactive, you may have high levels of TSH as your pituitary gland tries to stimulate the thyroid to produce more T3 and T4. And if your thyroid is overactive, your TSH may be abnormally low because your pituitary gland stops making TSH when your thyroid hormone levels are too high.
When should I get this test?
TSH is often the first test doctors order when they suspect you have a thyroid disorder. Both hypothyroidism and hyperthyroidism are common disorders. It is important to have your TSH checked if you have symptoms of these thyroid disorders. If so, your doctor may order a TSH or a thyroid panel test.
Symptoms of hypothyroidism include:
- Weight gain
- Feeling cold
- Painful joints and muscles
- Dry skin
- Thin and/or dry hair
- Slow heart rate
- Irregular menstrual periods
- Fertility problems
Symptoms of hyperthyroidism include:
- Weight loss
- Difficulty tolerating heat
- Mood swings
- Rapid or irregular heartbeat
- Loose, frequent bowel movements
TSH is also used to evaluate you if you are suspected to have other thyroid disorders, such as goiter, thyroid nodule, thyroid cancer, Graves’ disease, or Hashimoto’s thyroiditis. These disorders can cause hypothyroidism or hyperthyroidism.
Screening — testing without symptoms — with TSH for hypothyroidism in adults is controversial. It is most beneficial when early detection and treatment of disease help you avoid subsequent medical problems. Some organizations, such as the American Association of Clinical Endocrinology, the American Thyroid Association, and the Endocrine Society, favor routine screening for thyroid problems in adults without symptoms.
Other experts prefer screening only adults who are at increased risk of thyroid disorders, such as if you have autoimmune disorders or a family history of thyroid disease. The United States Preventive Services Task Force does not recommend screening for adults who are not pregnant. This task force believes there is not enough evidence that early thyroid disease detection results in better patient outcomes.
Because thyroid disorders can complicate pregnancy, screening with a TSH test during pregnancy is recommended for some women. Pregnant women without symptoms of thyroid problems may be screened if they:
- Have a family history of thyroid disease
- Live in an area where iodine deficiency is common
- Are over 30 years old
- Have a history of miscarriage, premature birth, or infertility
- Are significantly obese (with a body mass index over 40)
- Other risk factors are present
Newborn infants are routinely screened for congenital hypothyroidism, meaning an underactive thyroid that is present at birth. When caught early, the effects of hypothyroidism in infants can be successfully treated.
Blood levels of TSH will also be tested periodically in people who are being treated with replacement thyroid hormones due to hypothyroidism or because they’ve had surgery or radiation to the thyroid gland. By monitoring TSH, doctors can adjust the medication dose if necessary. Testing TSH may also be used to monitor you after hyperthyroidism treatment.
Finding a TSH Test
How can I get a TSH test?
TSH testing is most often performed at the doctor’s office or another medical setting like a laboratory or hospital. These tests are normally prescribed by a doctor but may be available without a doctor’s orders.
Can I take the test at home?
Several commercially available test kits allow you to provide a sample for TSH testing at home. Some kits test only TSH, and others test TSH in combination with other thyroid hormones or additional hormones, such as cortisol and free testosterone.
These kits may be purchased online and include the materials you need to take a finger-prick blood sample and return it to the company for testing. Your test results will be reported to you via a secure online platform.
At-home testing is convenient and can help you participate in your health care. But at-home tests cannot replace working with a health care provider. Share your concerns with your doctor if you have symptoms or are concerned your thyroid is not functioning properly. If an at-home test detects an abnormal TSH level, your doctor will likely retest the TSH and follow up with additional testing if the second TSH test is also abnormal.
How much does the test cost?
The cost of a TSH test will vary depending upon factors such as where it is performed and whether or not you have insurance coverage. Insurance will usually cover the cost of TSH testing if your doctor orders it to diagnose or treat a medical condition. You can check with your doctor, the lab, or your insurance company to learn more about the cost and what, if any, out-of-pocket costs you may be responsible for.
Taking a TSH Test
TSH testing requires a blood sample, which is usually taken from your arm in a doctor’s office, health clinic, hospital, or lab. Your doctor may recommend testing in the morning for the most accurate TSH result.
Before the test
Typically, no special preparations are needed prior to having a TSH test. It is a good idea to talk to your doctor about your medications, as certain medications may affect your test results.
If you are taking biotin or Vitamin B7 supplements, they should be discontinued at least two days before the TSH test, as they can interfere with the accuracy of your test results.
Multivitamins that contain small amounts of biotin are unlikely to interfere with the test results.
During the test
A blood sample is usually taken from a vein in your arm. The person drawing your blood may tie a band around your upper arm and will clean the area where the needle will enter your skin. A needle with a sample tube attached to it will be inserted into your vein, and a small amount of blood will be drawn into the tube. You may feel a slight sting when the needle pierces your skin.
TSH testing in a newborn involves taking a few drops of blood from the baby’s heel.
The process of taking a blood sample usually takes less than three minutes.
After the test
You will be asked to apply gentle pressure to the site where the blood was removed with a piece of gauze or bandage. The health provider will apply a bandage to the extraction site.
A blood draw is a very low-risk procedure. You may have slight bruising at the site where the blood sample was taken.
TSH Test Results
Receiving test results
Your doctor may share your test results with you, or you may be able to access them through an online portal. TSH results are often available within a few business days.
Interpreting test results
Your test results will indicate a blood level of TSH and whether it falls above or below normal limits, also called the reference range. Results are often reported in milli-international units per liter (mIU/L).
Reference ranges will vary slightly depending upon the laboratory used for the test. Additionally, there is some controversy in the medical community about what the upper limit of a normal TSH value should be and how to manage if you only have slightly elevated TSH levels.
The American Board of Internal Medicine uses an adult TSH reference range of 0.5–4.0 mIU/L. However, because they vary by laboratory, it’s important to ask your doctor about the reference range for your test results.
Doctors may take many factors into account when evaluating your TSH, including:
- Age: TSH levels tend to be higher if you are over the age of 80. Most older patients with slightly higher than normal TSH levels do not have any associated health problems.
- Pregnancy: Pregnancy causes changes in thyroid hormones. It is common for TSH to be slightly lower than normal during the first trimester, then slowly rise.
- Severe illness: If you are very sick with diseases not related to the thyroid you may have a low TSH temporarily.
- Other thyroid tests: The results of other tests, such as free T4 and thyroid antibodies, may also influence how a doctor interprets a TSH test.
A TSH value above the normal range may indicate the thyroid is underactive. When the TSH is below normal, it can be because the thyroid gland is making too much thyroid hormone. An abnormal TSH level is occasionally due to the pituitary gland not functioning correctly.
If you are being monitored for treatment of a thyroid condition, your doctor can tell you the target range in your case.
When you review the results of your TSH test with your doctor, it could be helpful to ask specific questions, such as the following:
- Is my level of TSH within the normal range?
- Do my test results suggest that my thyroid is overactive or underactive?
- What additional tests will you be ordering, if any?