Changing the diagnostic approach to diabetes insipidus: role of copeptin

Diabetes insipidus (DI) is characterized by polyuria and polydipsia. It can be caused either by deficit of vasopressin (central DI) or by renal resistance to its action (nephrogenic DI). The diagnosis of vasopressin deficiency can be confirmed by a serum osmolality >300 mOsm/kg and urine osmolality <300 mOsm/kg, while the differential diagnosis of different conditions presenting with polyuria and polydipsia with a serum osmolality <300 mOsm/kg requires a water deprivation test (1). Despite the fact that the water deprivation test represents the cornerstone for the diagnosis of DI (2), it is very distressing for patients and caregivers, exposes children to the risk of dehydration, it is time- consuming, its diagnostic accuracy is only 70%. Moreover, the following desmopressin test—used to evaluate the ability of the kidneys to concentrate urines in response to desmopressin—could be partially informative in patients with long-lasting polyuria and polydipsia.