Low levels of thyroid-stimulating hormone (TSH) indicate hyperthyroidism, a condition in which the thyroid is overactive. Symptoms include weight loss, fatigue, insomnia, increased heart rate, heat sensitivity and anxiety. There are an array of reasons for low TSH levels.
The pituitary gland produces TSH based on the amount of thyroxine (t4) and triiodothyronine (t3) in the bloodstream. Excessive t3 and t4 secretion stimulates low TSH production.
Reasons for low TSH levels include conditions such as goitre and Plummer's disease, which are identified by symptomatic adenomas. Adenomas are non-cancerous tumours causing thyroid enlargement, resulting in high thyroxine production, lowering TSH.
Graves' disease, an autoimmune condition, is a common reason for low TSH levels. Antibodies attack the thyroid, resulting in elevated thyroxine levels that decrease the amount of TSH secreted.
An inflamed thyroid defines an abnormality known as thyroiditis, which causes increased hormone secretion into the blood plasma, escalating thyroxine levels and decreasing TSH.
Hyperthyroidism occurring due to low TSH is diagnosed through blood tests that measure thyroxine and TSH levels in the bloodstream. Various therapies are available based on patient needs.