It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. TSH is made in a gland in the brain called the pituitary. When thyroid levels in your body are low, the pituitary gland makes more TSH.
When thyroid levels are high, the pituitary gland makes less TSH. TSH levels that are too high or too low can indicate your thyroid isn't working correctly. You may need a TSH test if you have symptoms of too much thyroid hormone in your blood hyperthyroidism , or too little thyroid hormone hypothyroidism. 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. 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 health care provider will let you know if there are any special instructions to follow.
A normal TSH value is generally defined as between. But opinions about this vary, since everyone has a personal "normal" that depends on their age and overall health. For example, your target level may be higher if you have heart disease or lower if you are pregnant.
A high TSH means different things depending on whether a person has known thyroid disease or not. A high TSH in people who are not undergoing thyroid disease treatment usually indicates the presence of primary hypothyroidism. This is by far the most common form of hypothyroidism , and it occurs because the thyroid gland produces an inadequate amount of thyroid hormones. The pituitary gland senses these low levels and increases the production of TSH.
An elevated TSH may also occur with normal thyroid function due to the presence of antibodies , proteins made by the immune system. A high TSH may be found in people being treated for either hypo- or hyperthyroidism. With hypothyroidism, a high TSH usually means that the dose of thyroid hormone replacement needs to be increased. In some cases, however, the dose is okay, but the medication is not being fully absorbed. For example, many foods and medications can affect the absorption of Synthroid levothyroxine in your system.
Learning what to avoid while taking this medication is important for it to work properly. With hyperthyroidism, a high TSH usually means that the treatment —be it surgery, radioactive iodine, or medications—was so effective in limiting the production of thyroid hormone it caused the person to become hypothyroid. A low TSH often means that a person has an elevated level of thyroid hormones.
Low TSH is most often associated with hyperthyroidism. This can be due to a number of causes, ranging from autoimmune disease to lumps in the thyroid gland toxic nodules to an abnormally enlarged thyroid gland goiter. It can also occur during a normal pregnancy as thyroid hormones are affected by "the pregnancy hormone" human chorionic gonadotropin HCG. Less often, a lack of TSH produced by the pituitary gland due to dysfunction can lead to low levels of thyroid hormone in the blood—a condition known as central hypothyroidism.
This is an exception to the general rule that hypothyroidism is associated with a high TSH. Central hypothyroidism is uncommon and usually associated with a deficiency of other pituitary hormones. This deficiency leads to a number of other symptoms as well. In people being treated for hypothyroidism, a low TSH level may mean:.
In people being treated for hyperthyroidism, a low TSH level usually means that further treatment is needed to reduce thyroid hormone levels. It could also mean that a person must continue to be monitored to make sure thyroid hormone levels return to normal. This is often the case for people who have temporary thyroiditis related to pregnancy or chemotherapy treatment.
There are a number of factors that can affect TSH levels. These are important to consider because lab values don't tell the whole story about someone's condition. A treatment plan that does not also consider someone's symptoms may prove to be ineffective. If a TSH test result is unexpected, simply repeating the test is often the best course of action.
Errors can occur during the blood draw, in transcribing the results, or due to mix-ups in the lab. Statistically, there is always a risk of lab error, and results should always be interpreted along with clinical symptoms and findings. A number of other factors can affect TSH test results , including:.
A capillary finger prick test, or blood spot test, is a somewhat controversial alternative to traditional TSH testing. It uses a finger prick rather than a standard blood draw from your vein to evaluate thyroid function. Blood spot testing kits have also been developed so that you can monitor your TSH level from home. Proponents of this test believe that it ensures greater accuracy without requiring as much of a sample as a venous blood draw.
However, since the test is not widely available right now, it's unknown exactly how well the test compares with conventional TSH testing. Do your part to help get the most accurate results by being as consistent as possible when it comes to the conditions under which you are tested.
For example, always have your test done at the same time of day, postpone your appointment if you are sick, and be sure you're always getting quality sleep. During diagnosis, most healthcare providers use the TSH test to evaluate thyroid function and determine the optimal course of treatment. There are times, however, when knowing one's TSH may be insufficient. For instance, free T4 in addition to TSH is usually tested if a healthcare provider suspects thyroid dysfunction due to disease of the pituitary gland or hypothalamus.
Likewise, if the TSH is normal, but a person still has symptoms of being hyperthyroid or hypothyroid, free T4 may be checked. TSH is also not necessarily sufficient to monitor hypothyroidism during pregnancy; T4 and free T4 are often recommended.
The doctor will monitor how well the treatment is working by running additional blood tests every few months. According to the Food and Drug Administration FDA , people should take levothyroxine once a day: in the morning and on an empty stomach, at least half an hour before eating.
They recommend that a person tells their doctor if they eat soybean flour, walnuts, dietary fiber, or cottonseed meal, as these can affect how the body processes levothyroxine.
Treatments for hyperthyroidism focus on reducing thyroid hormone levels to prevent long term health complications. A person may need to take beta-blockers and antithyroid medications. Another effective treatment is radioiodine therapy. This involves taking a capsule or liquid that contains radioactive iodine, which destroys cells that produce thyroid hormones.
However, people who take radioiodine therapy may develop hypothyroidism in the future. Surgical removal of the thyroid gland can treat severe hyperthyroidism. Doctors often reserve this for people who cannot take first-line medications, such as during pregnancy. A TSH test measures the amount of the hormone in the blood. Doctors can use the results to diagnose thyroid conditions, such as hypothyroidism and hyperthyroidism.
Reference ranges remain controversial, but for most people, the normal range falls between 0. Having an overactive or underactive thyroid can cause health issues that interfere with daily life.
During pregnancy, unusually high or low TSH levels can lead to complications. Some supplements that claim to boost thyroid health are now commercially available. However, they could lead to dangerous complications. Learn more. The thyroid gland produces hormones that affect metabolism, mood, breathing, heart rate, and more. Learn more about thyroid gland function.
At-home TSH tests offer an easy way for people to monitor their thyroid at home. Thyroid disorders may occur if the gland releases too much or too little hormone.
Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Diagnosis In general, your doctor may test for an underactive thyroid if you are feeling increasingly tired, have dry skin, constipation and weight gain, or have had previous thyroid problems or a goiter. Blood tests Diagnosis of hypothyroidism is based on your symptoms and the results of blood tests that measure the level of TSH and sometimes the level of the thyroid hormone thyroxine.
More Information Hypothyroidism diet Hypothyroidism: Can calcium supplements interfere with treatment? Hypothyroidism: Should I take iodine supplements? Soy: Does it worsen hypothyroidism? Show more related information. Request an Appointment at Mayo Clinic. More Information Coconut oil: Can it cure hypothyroidism? Share on: Facebook Twitter. Show references AskMayoExpert. Rochester, Minn. Chaker L, et al.
The Lancet. American Thyroid Association. Accessed Oct. Jameson JL, et al. In: Harrison's Principles of Internal Medicine.
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