A high TSH level indicates that the body does not have enough thyroid hormone. A TSH level lower than normal indicates there is usually more than enough thyroid hormone in the body and may indicate hyperthyroidism.

Is TSH increased or decreased in hyperthyroidism?

Thyroid-stimulating hormone (TSH) produced by the pituitary will be decreased in hyperthyroidism. Thus, the diagnosis of hyperthyroidism is nearly always associated with a low (suppressed) TSH level. If the TSH levels are not low, then other tests must be run. Thyroid hormones themselves (T3, T4) will be increased.

Why is TSH high in hyperthyroidism?

TSH prompts the thyroid to make more thyroid hormones in response to low levels. If the thyroid hormone levels are too high, referred to as hyperthyroidism or overactive thyroid, the pituitary will produce less TSH in an attempt to decrease production of active thyroid hormone.