Low Thyroid Symptoms
In some cases, there are no symptoms of low thyroid levels (this is called subclinical hypothyroidism). In such cases, the only way to tell if a person has an underactive thyroid is to perform a blood test that looks at certain thyroid hormone levels.
If left untreated, however, low thyroid levels may cause symptoms such as brittle nails; dry, coarse hair; a puffy face; weight gain; and heavy or irregular menstrual periods, among other things. Hypothyroidism affects several different areas of the body; thus, the symptoms also vary widely.
Hypothyroidism cannot be diagnosed on the basis of symptoms alone because many conditions share the same symptoms. This is also why blood tests are used to check for low thyroid levels. The two most common tests measure TSH and T4 levels in the blood. If TSH levels are too high or T4 levels are too low, a person likely has hypothyroidism.
(To learn more about the symptoms of an underactive thyroid, click Hypothyroidism Symptoms and Signs. This article lists other indications that a person has low thyroid hormone levels, as well as related conditions.)