What Are Thyroid Function Tests?

May 4, 2023

Thyroid function tests are blood tests that show how well the thyroid gland in the neck is producing thyroid hormone, and how much it has to be stimulated to do so.

What is TSH?

Thyroid stimulating hormone (TSH) is produced in the pituitary gland, located in the head. When the TSH is high, it can indicate that the thyroid gland is having difficulty producing enough thyroid hormone, and needs abnormally high levels of TSH to make it work. Low TSH levels can indicate high thyroid hormone levels turning off that particular pituitary function. Getting both tests tells how well both glands are working in concert. An appropriate thyroid screening test generally consists of only the TSH, because it is a very sensitive marker for hypothyroidism and hyperthyroidism. If it is abnormal, a free T3/T4 can be ordered.

What is T4?

A T4 or T3 test specifies the amount of thyroid hormone in the blood. A low level is known as hypothyroidism. This can result in fatigue, weight gain, cold intolerance, hair thinning, poor concentration, constipation, and dry skin. The opposite condition is hyperthyroidism. This can result in heat intolerance, fast heart beat, nervousness, and unexplained weight loss.

What are normal ranges for thyroid function test results?

Normal T4: 5.0 to 12.0 micrograms/dL

Normal TSH: 0.5 to 5.0 milli-international units per liter

Where can I order a thyroid test?

Many patients can have difficulty getting timely appointments with physicians. QuickMD now lets you order your own thyroid test online. The test can be collected at any LabCorp in the US, and one of the QuickMD doctors will contact you with the results.

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