Because hypothyroidism is more prevalent in older women, some doctors recommend that older women be screened for the disorder during routine annual physical examinations. Some doctors also recommend that pregnant women or women thinking about becoming pregnant be tested for hypothyroidism.
In general, your doctor may test for an underactive thyroid if you are feeling increasingly tired, have dry skin, constipation and weight gain, or have had previous thyroid problems or a goiter.
Diagnosis of hypothyroidism is based on your symptoms and the results of blood tests that measure the level of TSH and sometimes the level of the thyroid hormone thyroxine. A low level of thyroxine and high level of TSH indicate an underactive thyroid. That's because your pituitary produces more TSH in an effort to stimulate your thyroid gland into producing more thyroid hormone.
In the past, doctors weren't able to detect hypothyroidism until symptoms were fairly advanced. But by using the sensitive TSH test, doctors are able to diagnose thyroid disorders much earlier — often before you experience symptoms. Because the TSH test is the best screening test, your doctor will likely check TSH first and follow with a thyroid hormone test if needed. TSH tests also play an important role in managing hypothyroidism. They help your doctor determine the right dosage of medication, both initially and over time.
In addition, TSH tests are used to help diagnose a condition called subclinical hypothyroidism, which usually causes no outward signs or symptoms. In this condition, you have normal blood levels of triiodothyronine and thyroxine, but higher than normal levels of TSH.