Not Medical Advice: According to National Institute of Diabetes and Digestive and Kidney Diseases, Thyroid-Stimulating Hormone (TSH) blood test is used to check for thyroid gland problems, TSH is the key hormone for diagnosing hyperthyroidism and hypothyroidism.
This blood test is the most sensitive test of thyroid function available. The TSH test can detect TSH blood levels as low as 0.01 milli-international units per liter (mIU/L).
The normal range for TSH is between 0.3 and 4 mIU/L, although the range varies from one laboratory to another.
High TSH levels may be caused by:
An underactive thyroid (hypothyroidism). Hashimoto's thyroiditis is the most common cause of primary hypothyroidism.
A pituitary gland tumor that is making too much TSH. This is uncommon.
Not taking enough thyroid hormone medicine for treatment of an underactive thyroid gland.
Low TSH levels may be caused by:
An overactive thyroid gland (hyperthyroidism). Causes of hyperthyroidism include Graves' disease, a type of goiter (toxic multinodular goiter), or a noncancerous (benign) tumor called a toxic nodule.
Damage to the pituitary gland that prevents it from making TSH (a condition called secondary hypothyroidism).
Taking too much thyroid medicine for treatment of an underactive thyroid gland.
Pregnancy during the first trimester.
You can also learn more about TSH at WebMD.
Tip! Learn why a thyroid-stimulating hormone test is performed, what to expect during the test, and what the test results may mean at Healthline.com.