Normal Values:

Normal values are 0.4 - 4.0 mIU/L (milli-international units per liter).

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.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What abnormal results mean:

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)