What is normal TSH?

Answer 1

Normal values are from 0.4 to 4.0 mIU/L for those with no symptoms of abnormal thyroid function. 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 sometime 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.

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.

Answer 2

The normal TSH range varies in every laboratory and surprisingly the "normal range" is CONSTANTLY changing.

The most laboratories in the U.S. and many laboratories uses the REFERENCE RANGE 0.5 to 5.0 mIU/L as the norm. Levels below 0.5 indicate hyperthyroidism while levels above 5.0 indicate hypothyroidism.