Hypothyroidism means you have too little thyroid hormone. Another term is an “underactive thyroid.” Hypothyroidism is the most common thyroid disorder. It occurs more often in women and people over age 60. Hypothyroidism tends to run in families.
These symptoms are not unique to hypothyroidism. A simple blood test can tell whether the symptoms are due to hypothyroidism or some other cause. People with mild hypothyroidism may not have any symptoms at all.
In adults, untreated hypothyroidism leads to poor mental and physical performance. It also can cause high blood cholesterol levels that can lead to heart disease. A life-threatening condition called myxedema coma can develop if severe hypothyroidism is left untreated.
Diagnosis of hypothyroidism is especially important in pregnancy. Untreated hypothyroidism in the mother may affect the baby's growth and brain development.
All babies are tested at birth for hypothyroidism. If not treated promptly, a child with hypothyroidism could have an intellectual disability or fail to grow normally.
Blood tests can measure your levels of thyroid-stimulating hormone (TSH) and thyroid hormone (T4). You have hypothyroidism when you have high TSH and low T4 levels in your blood. In very early or mild hypothyroidism, TSH will be high but T4 may be normal. In this case, your doctor may measure the thyroid levels more frequently to determine if hypothyroidism develops over time.
When the cause of hypothyroidism is Hashimoto disease, blood tests can detect anti-thyroid antibodies that attack the thyroid.
Hypothyroidism is treated with thyroid hormone medication, taken as a pill. Levothyroxine is the drug of choice. It is a synthetic (laboratory-made) form of T4 that is identical to the T4 the thyroid naturally makes. Levothyroxine comes in brand-name and generic versions.
Most people need thyroid hormone replacement for life. If the brand or dosage needs to be changed, you should have blood tests for TSH done again. Your dose will be adjusted based on your TSH tests. Over time, doses of thyroid hormone that are too high can lead to bone loss, abnormal heart function, and abnormal heart rhythms. Doses that are too low may not relieve your symptoms.
Dose adjustment may be necessary over your lifetime, including during pregnancy. You can discuss dose changes during your regular check-ups with your doctor.
If you have one or more of the symptoms of hypothyroidism, or if thyroid disease runs in your family, ask your doctor if you should have a blood test. Doctors may also recommend testing in women over the age of 60, even if they don't have symptoms. If you are diagnosed with hypothyroidism, you will need treatment to avoid serious health problems.
Edited: September 2017
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