What Is Low TSH?

Low TSH refers to abnormally low levels of thyroid stimulating hormone in the bloodstream, potentially resulting from an array of conditions and causing a condition known as hyperthyroidism.

Significance

The thyroid secretes hormones thyroxine (t4) and triiodothyronine (t3) into the bloodstream. The pituitary gland releases amounts of thyroid stimulating hormone (TSH) based on the levels of thyroxine and triiodothyronine.

Function

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High levels of thyroxine and triiodothyronine occur due to abnormal thyroid function. Excessive amounts of thyroxine in the blood plasma decreases the production of TSH, leading to low TSH levels.

Causes

Low TSH is caused by conditions that increase thyroxine production such as Graves' disease, thyroiditis, and thyroid nodules, which are benign tumors symptomatic of Plummer's disease and goiter.

Effects

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Low THS levels cause abnormal thyroid function such as hyperthyroidism, a condition resulting in an overactive thyroid, with symptoms of weight loss, malaise, insomnia, elevated heart rate, temperature sensitivity and nervousness.

Diagnosis/Tests

Low TSH is diagnosed by evaluating pituitary hormone and TSH levels in the bloodstream. TSH testing includes: iodine uptake and thyroid scans, pituitary production and serum thyroid hormone measurements and TRH tests.