At a Glance
Why Get Tested?
When to Get Tested?
For screening: All newborns are screened for congenital hypothyroidism. There is currently no recommendation in the UK for routine screening of adults
For monitoring treatment: as directed by your doctor
Otherwise: when a patient has symptoms of hypo- or hyperthyroidism and/or an enlarged thyroid
A blood sample taken from a vein in the arm. For neonatal screening blood is collected by pricking the heel
Test Preparation Needed?
The Test Sample
What is being tested?
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.
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.
How is the sample collected for testing?
A blood sample obtained from a needle placed in a vein in your arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Ask a Laboratory Scientist
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.