What Are the Common Causes of Abnormal TSH Levels?

Abnormal thyroid stimulating hormone (TSH) levels are commonly caused by problems with the thyroid gland that result from hyperthyroidism or hypothyroidism. In these medical disorders, the levels of the thyroid hormones T₃ and, especially, T₄ are too high or too low. Numerous conditions can affect the production of thyroid hormones, and not many of them are particularly common.

Thyroid stimulating hormone isn’t produced by the thyroid gland. Instead, it's manufactured by the pituitary gland, and it has a stimulating and regulatory effect on the thyroid gland. The amount of thyroid stimulating hormone, as measured in a blood test, reflects what the pituitary "wants" the thyroid to do. A normal reading suggests good thyroid function, but abnormal TSH levels indicate the pituitary gland’s attempt to increase or decrease the hormones.

The most common and direct causes of abnormal TSH levels, therefore, are hypothyroidism and hyperthyroidism. Big increases in TSH are seen when thyroid hormones are low because the pituitary gland is attempting to stimulate production. When levels of the stimulating hormone are low, on the other hand, this is to discourage more production of T ₃ and T ₄, because there is already too much present in the body.

Hypothyroidism and hyperthyroidism don’t always result from the same causes. It’s not that uncommon for women to develop hypothyroidism. In most cases, there isn’t a specific dysfunction, like a node or swelling of the gland. A potential cause of hypothyroidism is an autoimmune disease called Hashimoto’s thyroiditis, which is more rare. Clearly, removing the thyroid gland also results in hypothyroidism.

The most common cause of hyperthyroidism is Graves' disease. Alternately, a small node on the thyroid gland can send it into overproduction, which might be suggested by low, abnormal TSH levels. Viruses can also result in hyperthyroidism, and about 5% of women develop a brief period of it after having a baby.

Other potential causes of high or low hormone levels are the use of the medications lithium and amiodarone. Thyroid cancer is relatively rare, but it is likely to result in abnormal TSH levels. Readings for TSH will fall outside of normal in some patients undergoing radiation therapy for cancer.

It's important to note that abnormal TSH levels are sometimes due to a poorly conducted or flawed test. If a person is completely free of symptoms, it is a good idea to repeat the test. This can confirm or invalidate the original results and direct doctors toward appropriate interventions, if required.