Which laboratory finding is indicative of diabetes insipidus?

A serum osmolality greater than 300 mOsm/kg is indicative of diabetes insipidus because this condition is characterized by an inability of the kidneys to concentrate urine due to a deficiency of antidiuretic hormone (ADH) or a lack of response to it. In diabetes insipidus, individuals typically produce large volumes of dilute urine, leading to a higher concentration of solutes in the serum and thus increased serum osmolality.

This lab finding helps in differentiating diabetes insipidus from conditions such as syndrome of inappropriate antidiuretic hormone (SIADH), where serum osmolality would be low due to excessive ADH leading to concentrated urine. The serum osmolality measurement is crucial in the assessment and management of this condition, guiding further diagnostic steps and interventions.

In contrast, urine specific gravity greater than 1.030 suggests concentrated urine, which is not typical of diabetes insipidus. Increased serum potassium levels are not specifically associated with diabetes insipidus and can occur in various other conditions. Decreased blood urea nitrogen would also not be indicative of diabetes insipidus, as this condition primarily affects water balance and osmolality rather than urea production or concentration.