Which condition is characterized by an underactive thyroid gland?

Hypothyroidism is characterized by an underactive thyroid gland, which means that the thyroid does not produce enough thyroid hormones (primarily thyroxine, or T4, and triiodothyronine, or T3) to meet the body's needs. This condition can lead to a variety of symptoms such as fatigue, weight gain, cold intolerance, dry skin, hair loss, and depression, among others.

The underactivity of the thyroid gland can result from several causes, including autoimmune diseases like Hashimoto's thyroiditis, iodine deficiency, certain medications, or damage to the thyroid from surgery or radiation. The diagnosis of hypothyroidism is typically confirmed through blood tests that measure levels of thyroid hormones and Thyroid Stimulating Hormone (TSH), which often shows elevated TSH levels alongside low T4 levels.

Understanding the characteristics and implications of hypothyroidism is crucial in endocrinology, especially given its prevalence and the need for management to ensure a patient's quality of life.