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What Does a Low TSH Mean?

Thyroid stimulating hormone (TSH) is secreted by the pituitary gland. The function of TSH is to stimulate the thyroid to produce more thyroid hormone.

  1. Low TSH

    • A low TSH level means too much thyroid hormone is circulating in your blood.

    How It Happens

    • When your thyroid gland is overactive and producing too much thyroid hormone (hyperthyroidism), your pituitary gland decreases the amount of TSH to slow down production of thyroid hormone, creating a low TSH level.

    Causes

    • According to the University of Michigan Health System, possible causes of hyperthyroidism are taking too much thyroid replacement hormone, an infected or inflamed thyroid gland, a thyroid gland that has grown too large or a tumor in the thyroid gland that is producing extra thyroid hormone.

    Additional Testing

    • If your TSH level is low, your doctor may do additional testing to find the cause.

    Considerations

    • According to the Alt.Support.Thyroid Newsgroup, testing TSH doesn't always provide an accurate indicator of thyroid health. Because TSH is a pituitary hormone, if the pituitary gland or the hypothalamus (which controls the pituitary) has a problem, TSH could test normal, but your thyroid hormones (T4 and T3) could be too low or too high.

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