Thyroid stimulating hormone is released by the pituitary gland to control the thyroid, which makes it the standard first-line test for thyroid function. A raised TSH usually points to an underactive thyroid and a low TSH to an overactive one. The test costs £71.25 plus the £50 phlebotomy fee, and results are usually available in 1 day.
No fasting is needed. If you take levothyroxine, many clinicians advise taking the dose after the blood sample on the day of the test so the result reflects your usual level.
TSH reflects how hard the pituitary is asking the thyroid to work. High TSH suggests an underactive thyroid and low TSH an overactive thyroid.
Many clinicians suggest taking levothyroxine after the blood is drawn on test day. Follow the advice of the clinician who prescribes it.
TSH is the first-line screen. If it is abnormal, or if you have symptoms with a normal TSH, a fuller thyroid profile with free T4 and free T3 gives more detail.
Results are usually available in 1 day by email.