What TSH level indicates hypothyroidism?

Hypothyroidism is commonly characterized by an elevated level of Thyroid Stimulating Hormone (TSH) due to the body's attempt to stimulate the thyroid gland when thyroid hormones (T3 and T4) are low. In general, a TSH level that exceeds the upper limit of the normal range indicates an underactive thyroid.

The normal reference range for TSH is usually around 0.4 to 4.0 mIU/L, although this can vary slightly based on the laboratory and specific populations. A TSH level above 4.0 mIU/L often suggests hypothyroidism, particularly levels ranging from 5.1 to 10.0 mIU/L, which indicate a more definitive diagnosis of hypothyroidism.

A TSH level above 10.0 mIU/L points to overt hypothyroidism, where the deficiency of thyroid hormones is significant enough to markedly elevate TSH. Hence, while TSH levels in the range of 5.1 to 10.0 indicate hypothyroidism, levels above 10.0 suggest a more severe form of hypothyroidism.

In this context, the choice of TSH levels that includes 5.1 to 10.0 as indicative of hypothyroidism