A TSH level measures the amount of thyroid-stimulating hormone in the blood. This hormone, which is made in the pituitary gland, triggers the thyroid gland to release the hormones T4 and T3.
A TSH level is drawn to monitor the effectiveness of thyroid hormone replacement medications and to diagnose a thyroid disorder or pituitary dysfunction.
A blood sample for a TSH level is drawn by a phlebotomist or nurse from a vein in your arm or hand. The blood sample is sent to a laboratory for processing. Fasting is not required before having a TSH level drawn.
According the MedlinePlus.com, a normal TSH level is between 0.4 and 4.0 mlU/L. If you have a thyroid disorder and are receiving treatment, your physician may want to keep your thyroid level between 0.5 and 3.0 mlU/L.
Different laboratories may have slightly different normal ranges for a TSH level. Your physician will decide if your TSH level is abnormal.
An increased level of TSH may indicate thyroid dysfunction, infection of the thyroid gland, thyroid agenesis and congenital cretinism. A decreased TSH level may indicate pituitary dysfunction and hyperthyroidism.