Worldwide, too little iodine in the diet is the most common cause of hypothyroidism.[1][8] Hashimoto's thyroiditis is the most common cause of hypothyroidism in countries with sufficient dietary iodine.[3] Less common causes include previous treatment with radioactive iodine, injury to the hypothalamus or the anterior pituitary gland, certain medications, a lack of a functioning thyroid at birth, or previous thyroid surgery.[3][9] The diagnosis of hypothyroidism, when suspected, can be confirmed with blood tests measuring thyroid-stimulating hormone (TSH) and thyroxine levels.[3]