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Reasons for Low TSH

The pituitary gland produces thyroid stimulating hormone (TSH), which boosts the thyroid's secretion of hormones thyroxine (T4) and triiodothyronine (T3), affecting metabolism, heart rate, body temperature and protein production. Low TSH levels indicate hyperthyroidism, which has an array of causes.

  1. Hyperthyroidism

    • An abnormally functioning thyroid produces low or high levels of TSH, depending on the amount of thyroxine secreted into the blood serum. High thyroxine and low TSH identify an overactive thyroid (hyperthyroidism).

    Graves' Disease

    • Graves' disease is an autoimmune disease in which the thyroid is attacked by antibodies that stimulate high production of the hormone thyroxine (T4). The result of high thyroxine is low TSH.

    Adenomas

    • Adenomas are benign tumors that can cause the thyroid to enlarge, which can stimulate abnormally high thyroxine productions, lowering TSH levels.

    Thyroiditis

    • Thyroiditis is a condition in which the thyroid gland swells and secretes hormone into the blood plasma. This process heightens levels of thyroxine in the blood, which in turn cause low TSH.

    Diagnosis/Treatment

    • Low TSH is diagnosed through blood tests that measure thyroxine and TSH levels. Treatments of low TSH (hyperthyroidism) include radioactive iodine, anti-thyroid therapy, beta blockers and thyroidectomy.

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