What laboratory finding would suggest the development of diabetes insipidus (DI) in a client with a head injury?

The presence of a serum sodium level of 155 mEq/L indicates hypernatremia, which is a key laboratory finding suggestive of diabetes insipidus (DI). In DI, there is a deficiency in the production or response to antidiuretic hormone (ADH), leading to excessive urination (polyuria) and, therefore, elevated serum sodium due to the loss of free water. This imbalance results in a higher concentration of sodium in the blood, hence the elevated serum sodium level.

Additionally, urine output in DI is significantly increased, which may also contribute to a higher serum sodium concentration as the body loses more water. The normal response of the kidneys in the presence of ADH would be to concentrate the urine; however, in the case of DI, the urine remains dilute, leading to an elevated serum sodium level.

Other choices reflect urine and serum findings that do not align with the typical laboratory markers of diabetes insipidus. For example, a urine specific gravity of 1.025 is often within the normal range, indicating that the urine is relatively concentrated, which is not consistent with DI. A serum potassium level of 4.2 mEq/L falls within the normal range and is not indicative of DI. Lastly,