Thyroid Stimulating Hormone (TSH)
The hypothalamus produces a substance called Thyrotropin-Releasing Hormone (TRH). The pituitary gland is stimulated by TRH and produces the Thyroid Stimulating Hormone (TSH). The thyroid gland, in turn, is stimulated by the TSH to produce two hormones: thyroxine (T4) and triiodothyronine (T3). These two hormones help in controlling the metabolism of the body. The thyroid Stimulating Hormone Test measures the levels of TSH in the blood.
Why is the test ordered?
The test may be ordered to determine whether the thyroid gland is working properly or not. The test may also be recommended to determine the cause of hypothyroidism and monitor its treatment, as well as to monitor thyroid gland function in people who are being treated for hyperthyroidism. The test can be used for newborn babies to determine the presence of an underactive thyroid gland.
How is the sample collected?
A blood sample is collected from a vein in the arm.
How to prepare for the test?
There is no special preparation required for the test, although it is advisable to inform the doctor about all the medicines or supplements that the patient is taking before getting the test done. For those who are on thyroid hormone therapy, their blood has to be drawn before they take the dose for that day. It is better to inform the doctor if the person who would be undergoing the test has had an X-ray done recently by taking radioactive material or iodine dye, about four to six weeks prior to taking the test. Results of the Thyroid Stimulating Hormone Test may not be accurate for a person who has had iodine contrast prior to the test.