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Hypothyroidism is the condition that results when the thyroid gland does not produce enough thyroid hormone. Thyroid hormone is a chemical messenger used by the brain to regulate metabolism, which is the way the body uses energy.
Subclinical hypothyroidism is a very mild type of hypothyroidism which does not produce the normal symptoms of hypothyroidism. Subclinical hypothyroidism shows in blood tests with normal levels of thyroxine, which is the main kind of thyroid hormone, but higher than normal levels of TSH or thyroid-stimulating hormone. This means the body is putting out more TSH than normal to get the thyroid gland to produce the needed amount of thyroxine.
Although subclinical hypothyroidism does not produce recognizable symptoms, it can have serious consequences if left untreated. An article published in JAMA, the Journal of the American Medical Association, reported that patients with subclinical hypothyroidism, especially those with higher levels of TSH (over 10mU/L) are at increased risk of coronary heart disease or heart failure.
Other studies show that people with subclinical hypothyroidism are twice as likely to develop congestive heart failure. This condition occurs when the heart is not able to pump enough blood to the other organs in the body. The results can be fatigue, swollen ankles, difficulty breathing, and eventual failure of the heart causing death. (American Thyroid Association)
Pregnant women who have subclinical hypothyroidism are also at higher risk for complications during their pregnancy. As in other patients with subclinical hypothyroidism, pregnant women often have no symptoms even though blood tests show abnormal thyroid hormone levels. These women may have a higher risk of miscarriage, pre-eclampsia (high blood pressure), and preterm delivery. Babies whose mothers have subclinical hypothyroidism are also at risk for developmental delays. (MedicineNet)
Subclinical hypothyroidism can generally be treated with a daily dose of the thyroid hormone thyroxine.