The normal range of TSH levels in non-pregnant adult women is 0.5 to 5.0 mIU/L. A TSH level higher than 5.0 usually indicates an underactive thyroid (hypothyroidism) and a TSH level lower than 0.4 indicates the presence of excessive thyroid hormone and overactive thyroid (hyperthyroidism) . However, experts do not agree on which TSH levels should be considered too high. Some suggest that TSH levels of over 2.5 milliunits per liter (mU/L) are abnormal, while others consider levels of TSH to be too high only after they have reached 4 to 5 mU/L. A level of 10 mIU/L or higher is considered full-blown hypothyroidism.

It is important to note that TSH levels vary by stage of life and sex. The normal TSH slowly increases as people get older, and a TSH level of 7 would be considered high enough in a 20-year-old to need treatment. That same number might be considered normal in someone who is 70 or 80 years old.