Thyroid-stimulating Hormone (TSH)

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 alone 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, which is a lump on the thyroid gland
• To evaluate a goiter, which is enlargement of the thyroid gland
• To diagnose or rule out thyroid diseases, such as Hashimoto’s thyroiditis, Graves’ disease, and thyroid cancer
• To monitor a patient’s response to treatment for hypothyroidism, hyperthyroidism, or another thyroid condition

What does the test measure?

The TSH test measures thyroid-stimulating hormone, which is a hormone that prompts the thyroid to produce other hormones. The thyroid is a butterfly-shaped gland in your neck that makes the hormones triiodothyronine (T3) and thyroxine (T4). T3 and T4 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. The pituitary gland is sometimes called “the master gland,” because it produces many hormones that control the functions of other glands in the body. The pituitary gland is able to 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. 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 a TSH test?

TSH is often the first test doctors order when they suspect a patient has a thyroid disorder. Both hypothyroidism and hyperthyroidism are common disorders. All patients with symptoms of these thyroid disorders should have their TSH checked.

If you are having symptoms of these disorders, your doctor may order a TSH or a thyroid panel test. Symptoms of hypothyroidism include:

• Fatigue
• Depression
• Weight gain
• Feeling cold
• Painful joints and muscles
• Dry skin
• Thin and/or dry hair
• Slow heart rate
• Constipation
• Irregular menstrual periods
• Fertility problems

Symptoms of hyperthyroidism include:

• Weight loss
• Irritability
• Anxiety
• Insomnia
• Difficulty tolerating heat
• Mood swings
• Rapid or irregular heartbeat
• Loose, frequent bowel movements

TSH is also used to evaluate patients who 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 with TSH for hypothyroidism in adults is controversial. Screening means testing in the absence of symptoms. It is most beneficial when early detection and treatment of disease helps people 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 favor screening only adults who are at increased risk of thyroid disorders, such as people with 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 detection of thyroid disease results in better outcomes for patients.

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 are able to adjust the medication dose if necessary. Testing TSH may also be used to monitor patients after they have been treated for hyperthyroidism.

How to get tested

TSH testing is most often performed at the doctor’s office or another medical setting like a laboratory or hospital. TSH tests are normally prescribed by a doctor but may be available without a doctor’s orders.

Can I take the test at home?

Several test kits are commercially available that 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 sample of blood 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. If you have symptoms or are concerned that your thyroid is not functioning properly, be sure to share your concerns with your doctor. If an at-home test detects an abnormal TSH level, your doctor is likely to 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.

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 any medications you are taking, 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. A bandage will be applied 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.

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 thyroid-stimulating hormone (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 patients who have only 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 a number of factors into account when evaluating a patient’s TSH, including:

• Age: TSH levels tend to be higher in patients 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: People who are very sick with diseases that are not related to the thyroid 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 that the thyroid is underactive. When the TSH is below normal, it can be because the thyroid gland is making too much thyroid hormone. Occasionally, an abnormal TSH level is due to the pituitary gland not functioning correctly.

If you are being monitored for treatment of a thyroid condition, your doctor can tell you what the target range is in your case.

Are test results accurate?

Although no test is 100% correct all the time, your TSH test is likely to reflect your level of thyroid-stimulating hormone accurately. Most labs now use a highly precise, third-generation testing process for TSH. This method of testing is accurate to within 0.01 mIU/L. Some labs use an older, second-generation testing method, which is accurate to within 0.1 mIU/L.

It is important to bear in mind that thyroid tests are a snapshot of what is going on in your body at the moment the test sample is taken. Your TSH levels may fluctuate based on factors discussed above, such as pregnancy, illness, and age.

Do I need follow-up tests?

An abnormal result on a TSH test may lead to further testing of your thyroid function. Often, the TSH is retested, and the thyroid hormone free T4 is measured as well. Your doctor may order a thyroid panel that includes several thyroid hormone tests. Some patients will also have thyroid antibody tests. Antibody tests may reveal whether autoimmune disorders like Graves’ disease or Hashimoto’s thyroiditis are causing an overactive or underactive thyroid.

Questions for your doctor about test results

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?

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