Your thyroid stimulating hormone (TSH) level is low. Normal is between 0.3 and 4.0, with each laboratory reporting different ranges.
Almost always, a low TSH means that you have too much thyroid hormone in your blood. This could be caused by:
- An overactive thyroid gland (hyperthyroidism)
- Taking a dose of thyroid medication that is more than you need
Here is the explanation: Thyroid stimulating hormone is made by the pituitary gland. This small gland sits at the bottom of the brain. The gland sends TSH into the blood stream. When TSH reaches the thyroid gland, it causes the thyroid to make thyroid hormone.
The amount of thyroid hormone in the blood is relatively constant. If the level is normal, TSH will be normal. If the blood level of thyroid hormone rises above the normal range, the pituitary gland slows down and makes little or no TSH. The TSH level gets very low.
However, sometimes the pituitary gland is damaged or not functioning normally. In this case, the gland makes little or no TSH, so the blood level is very low. Without TSH in the blood, the thyroid gland does not get stimulated to make thyroid hormone. So, the blood level of thyroid hormone also gets very low. And now you have hypothyroidism.