A glance at TSH（Thyroid-stimulating hormone）

Why do we test TSH?

Via AACC

The thyroid gland, or simply the thyroid, is an endocrine gland in the neck, consisting of two lobes connected by an isthmus. It is found at the front of the neck, below the Adam's apple. The thyroid gland secretes thyroid hormones, which primarily influence the metabolic rate and protein synthesis. The hormones also have many other effects including those on development.

Via AACC

Why Get Tested?

To screen for and help diagnose thyroid disorders; to monitor treatment of hypothyroidism and hyperthyroidism

When to Get Tested?

For screening: Newborn screening is widely recommended; however, there is no consensus within the medical community as to the age adult screening should begin or whether screening should be done.

For monitoring treatment: as directed by your healthcare provider

Otherwise: when a person has symptoms of hyperthyroidism or hypothyroidism and/or an enlarged thyroid

Sample Required?

A blood sample drawn from a vein in your arm or from pricking the heel of an infant

Test Preparation Needed?

None needed; however, certain medications can interfere with the TSH test, so tell your health practitioner about any drugs that you are taking. If you take thyroid hormone as treatment for thyroid disease, it is recommended that your blood sample be drawn before you take your dose for that day.

How is it used?

The thyroid-stimulating hormone (TSH) test is often the test of choice for evaluating thyroid function and/or symptoms of a thyroid disorder, including hyperthyroidism or hypothyroidism.

TSH is produced by the pituitary gland, a tiny organ located below the brain and behind the sinus cavities. It is part of the body's feedback system to maintain stable amounts of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the blood and to help control the rate at which the body uses energy.

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

When is it ordered?

A health practitioner may order a TSH test when someone has symptoms of hyperthyroidism or hypothyroidism and/or when a person has an enlarged thyroid gland (goiter).

Signs and symptoms of hyperthyroidism may include:

• Increased heart rate

• Anxiety

• Weight loss

• Difficulty sleeping

• Tremors in the hands

• Weakness

• Diarrhea (sometimes)

• Light sensitivity, visual disturbances

• 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:

• Weight gain

• Dry skin

• Constipation

• Cold intolerance

• Puffy skin

• Hair loss

• Fatigue

• 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.

What does the test result mean?

A high TSH result may mean that:

• The person tested has an underactive thyroid gland that is not responding adequately to the stimulation of TSH due to some type of acute or chronic thyroid dysfunction

• A person with hypothyroidism or who has had their thyroid gland removed is receiving too little thyroid hormone replacement medication and the dose may need to be adjusted

• A person with hyperthyroidism is receiving too much anti-thyroid medication and the dose needs adjusting

• There is a problem with the pituitary gland, such as a tumor producing unregulated levels of TSH

A low TSH result may indicate:

• An overactive thyroid gland (hyperthyroidism)

• 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