People concerned about their thyroid functioning can visit their primary care doctors to discuss their concerns and have their thyroid levels checked through blood tests, explains WebMD. Tests are available to test thyroid-stimulating hormone, or TSH, as well as the hormones the thyroid directly secretes.
The pituitary gland releases thyroid-stimulating hormone to trigger the thyroid gland to produce hormones, states WebMD. TSH levels are high in individuals who suffer from hypothyroidism, or an underactive thyroid, because their pituitary glands are trying to stimulate their thyroids to produce the hormones they are failing to secrete. Conversely, those who suffer from hyperthyroidism, or an overactive thyroid gland, exhibit abnormally low TSH levels. This occurs because their thyroids are already producing excess amounts of hormones, and there is no need for their pituitary glands to attempt to get them to produce more.
The hormones the thyroid is responsible for producing are thyroxine, abbreviated as T4, and triiodothyronine, abbreviated as T3, notes WebMD. Tests for levels of these hormones are commonly performed after an initial test shows abnormal levels of TSH to help determine the source of the problem. Three T4 tests, called the total thyroxine, free thyroxine and free thyroxine index tests, are also useful in determining how well the treatment of a thyroid problem is working.