What condition is suggested by low urine osmolality with high serum osmolality?

Low urine osmolality combined with high serum osmolality is indicative of Diabetes Insipidus. In this condition, the kidneys are unable to concentrate urine due to a deficiency of antidiuretic hormone (ADH) or due to insensitivity to ADH. As a result, the urine becomes dilute, leading to low urine osmolality.

Simultaneously, the serum osmolality remains elevated because the body's ability to conserve water is impaired, resulting in the excretion of large volumes of dilute urine while the serum concentration increases. This reflects the characteristic findings of Diabetes Insipidus, where the patient often experiences excessive thirst and urination, contributing to the derangement in serum osmolality.

In contrast, Diabetes Mellitus typically presents with high serum glucose levels, which can lead to hyperosmolarity, but it does not primarily affect urine osmolality in the same manner as seen in Diabetes Insipidus. Hypernatremia refers to a high sodium concentration in the serum and could accompany high serum osmolality but does not explain the low urine osmolality without the context of fluid regulation issues, while hyponatremia involves low serum sodium, which would not correlate with high serum osmolality.