Serum TSH

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Serum TSH Test

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

When this Serum TSH test is required

Your doctor requests this test if you show symptoms of a thyroid disorder. For example, symptoms of hyperthyroidism include heat intolerance, weight loss, rapid heartbeat, nervousness, insomnia, and breathlessness. Common symptoms of hypothyroidism include fatigue, weakness, weight gain, slow heart rate, and cold intolerance.The test may also be requested to monitor the effectiveness of treatment when a patient is being treated for a known thyroid disorder.The blood test may be requested with other thyroid hormone tests and after a physical examination of your thyroid. TSH screening is routinely performed in newborns. There are currently no recommendations for routine screening of adults in the UK.

What the Serum TSH Test Detects

The test measures the amount of thyroid-stimulating hormone (TSH) in your blood, which is an indicator of thyroid disease. TSH is made 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.Together these tests are referred to as thyroid function tests.Thyroid hormones help control the rate at which the body uses energy. When concentrations decrease in the blood, the hypothalamus (an organ in the brain) releases thyrotropin releasing hormone (TRH). This stimulates the release of TSH by the pituitary gland. The TSH in turn stimulates the production and release of T4 and T3 by the thyroid gland, a small butterfly-shaped gland that lies in the neck flat against the windpipe. When all three organs are functioning normally, thyroid hormone concentrations in the blood remain constant.See MoreSee Less

Preparation for the Serum TSH Test

None required

Sample Requirements

A blood sample taken from a vein in the arm. For neonatal screening blood is collected by pricking the heel

Additional Notes

Thyroid-hormone replacement therapy and some drugs may interfere with thyroid function test results, so tell your doctor about any drugs you are taking, for example, lithium and amiodarone.When your doctor adjusts your dose of thyroid hormone, it is important that you wait at least 6 weeksone to two months before checking your TSH again, so that your new dose can have its full effect.Extreme stress and acute illness may also affect TSH test results, and results may be low during the first trimester of pregnancy.

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