What is the hallmark symptom of diabetes insipidus?

The hallmark symptom of diabetes insipidus is excessive water loss in urine, which results in the production of large volumes of dilute urine. This condition arises from a deficiency in the production of vasopressin (also known as antidiuretic hormone, ADH) or the body's inability to respond to it. When ADH is insufficient, the kidneys cannot properly concentrate urine, leading to an inability to conserve water. As a consequence, individuals with diabetes insipidus experience significant polydipsia (increased thirst) to compensate for the fluid loss, but ultimately, they lose a substantial amount of water, which can lead to dehydration if not managed appropriately.

In contrast, while high blood sugar levels are associated with diabetes mellitus, they are not a feature of diabetes insipidus. Mild hypertension and low calcium levels do not relate to the primary pathophysiological changes leading to diabetes insipidus. Therefore, the defining characteristic of this condition is clearly the excessive production of dilute urine, marking it as the primary symptom to be recognized.