Thyroid Physiology — Feedback Loops

An elevated TSH usually means that too little thyroid hormone is circulating (Hypothyroidism), so the hypothalamus is telling the pituitary to put out extra TSH to try to get the Thyroid Gland moving.

A low TSH usually means that so much thyroid hormone is circulating (Hyperthyroidism), that the hypothalamus tries to shut down pituitary production