In people with mild thyroid underactivity, higher levels of TSH are linked to higher ratios of neutrophils to lymphocytes, which may reflect increased systemic inflammation.

In people with thyrotoxicosis caused by taking too much thyroid hormone medication, the brain's control system for thyroid hormone levels behaves differently than in people whose thyroid gland overproduces hormones on its own. Specifically, TSH stays low even when thyroid hormone levels are higher than normal.

When someone has Graves’ disease, their thyroid hormones get too high, which tells the brain to stop making a hormone that stimulates the thyroid — so that hormone ends up being very low or even missing in blood tests.

In people with thyroid diseases, higher levels of TSH in the blood are linked to lower amounts of iodine, selenium, and zinc in the thyroid tissue, indicating that thyroid function may be related to the balance of these trace elements.

In adults taking thyroid hormone medication, consistently having too much hormone in the blood—measured by very low TSH or high free thyroxine—is linked to a higher chance of developing heart failure.

People in India who start getting gray hair earlier than usual tend to have higher levels of a thyroid hormone marker in their blood, even if they don’t feel sick or show other signs of thyroid problems.