Despite its small size, the thyroid gland is rightly considered one of the most important "workers" of the endocrine system. If it is healthy, then we will not lack in mental alertness, ease of movement, positive mood and even a slim figure. Only blood hormone level tests, thyroid ultrasound, radiography with radioactive iodine can tell us with a high degree of certainty that it is unhealthy; in some cases, a biopsy is prescribed.