The thyroid gland lies at the base of the neck. It produces a hormone called thyroxine which regulates cell activity throughout the body.
Several disorders can cause the thyroid to produce too much or too little thyroxine.
Hyperthyroidism is too much hormone. Hypothyroidism is too little hormone. These conditions can result from inflammation, cysts, or cancer of the thyroid. A goiter is an enlarged or swollen thyroid gland. The tests often include thyroid stimulating hormone, or TSH, which comes from the brain.