A TSH test is frequently ordered along with or preceding a free T4 test. Other thyroid tests that may be ordered include a free T3 test and thyroid antibodies (if autoimmune-related thyroid disease is suspected). Sometimes TSH, free T4 and free T3 are ordered together as a thyroid panel.
TSH testing is used to:
Diagnose a thyroid disorder in a person with symptoms
Screen newborns for an underactive thyroid
Monitor thyroid replacement therapy in people with hypothyroidism
Monitor anti-thyroid treatment in people with hyperthyroidism
Help diagnose and monitor infertility problems in women
Help evaluate the function of the pituitary gland (occasionally)
Screen adults for thyroid disorders, although expert opinions vary on who can benefit from screening and at what age to begin
The eyes may be affected: puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes.
Signs and symptoms of hypothyroidism may include:
Menstrual irregularity in women
TSH may be ordered at regular intervals when an individual is being treated for a known thyroid disorder. When a person's dose of thyroid medication is adjusted, the American Thyroid Association recommends waiting 6-8 weeks before testing the level of TSH again.
TSH screening is routinely performed in the United States on newborns soon after birth as part of each state's newborn screening program.
In 2004, the U.S. Preventive Services Task Force found insufficient evidence to recommend for or against routine screening for thyroid disease in asymptomatic adults. However, the American Thyroid Association and the American Association of Clinical Endocrinologists released clinical practice guidelines in 2012 that recommend that screening for hypothyroidism should be considered in people over the age of 60. Because the signs and symptoms of both hypothyroidism and hyperthyroidism are so similar to those seen in many common disorders, health practitioners often need to rule out thyroid disease even though the patient has another problem.
Excessive amounts of thyroid hormone medication in those who are being treated for an underactive (or removed) thyroid gland
Insufficient anti-thyroid medication in a person being treated for hyperthyroidism; however, it may take a while for TSH production to resume after successful anti-thyroid treatment. This is why the American Thyroid Association recommends monitoring this treatment with tests for thyroid hormones (T4 and T3) as well as TSH levels.
Damage to the pituitary gland that prevents it from producing adequate amounts of TSH
Whether high or low, an abnormal TSH indicates an excess or deficiency in the amount of thyroid hormone available to the body, but it does not indicate the reason why. An abnormal TSH test result is usually followed by additional testing to investigate the cause of the increase or decrease.
The following table summarizes some examples of typical test results and their potential meaning.
It is important to note that TSH, free T4, and free T3 tests are a "snapshot" of what is occurring within a dynamic system. An individual person's thyroid testing results may vary and may be affected by:
Increases, decreases, and changes (inherited or acquired) in the proteins that bind T4 and T3
Many medications — including aspirin and thyroid-hormone replacement therapy — may affect thyroid gland function test results and their use should be discussed with the health practitioner prior to testing.
Illnesses not directly related to the thyroid, "nonthyroidal illnesses," can affect thyroid hormones levels. In particular, the level of T3 can be low in nonthyroidal illness (NTI). Typically, the thyroid hormone levels return to normal after a person recovers from the nonthyroidal illness. Historically, this condition was referred to as "euthyroid sick syndrome" but that term is controversial because there is some question as to whether those affected have a thyroid gland that is functioning normally (euthyroid).
When a health practitioner adjusts a person's thyroid hormone replacement dosage, it is important to wait at least one to two months before checking the TSH again so that the new dose can have its full effect.
Extreme stress and acute illness may affect TSH test results. It is generally recommended that thyroid testing be avoided in hospitalized patients or deferred until after a person has recovered from an acute illness.
Results may be low during the first trimester of pregnancy.
This article was last reviewed on October 15, 2014. | This article was last modified on March 11, 2015.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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