Normal values are 0.4 - 4.0 mIU/L.

However, those without signs or symptoms of an underactive thyroid who have a TSH value over 2.0 mIU/L but normal T4 levels may develop hypothyroidism in the future. This is called subclinical hypothyroidism (mildly underactive thyroid) or early-stage hypothyroidism. Anyone with a TSH value above this level should be followed very closely by a doctor.

If you are being treated for a thyroid disorder, your TSH level should be between 0.5 and 3.0 mIU/L.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Greater than normal levels may indicate:

• Congenital hypothyroidism (cretinism)
• Exposure to mice (lab workers or veterinarians)
• Primary hypothyroidism
• Thyroid hormone resistance
• TSH-dependent hyperthyroidism

Lower than normal levels may be due to:

• Hyperthyroidism
• TSH deficiency
• Use of certain medications (including dopamine agonists, glucocorticoids, somatostatin analogues, and bexarotene)