In a patient with diabetes insipidus, what is the most important reason to monitor serum sodium?

• A. To prevent seizures
• B. To monitor kidney function
• C. To track fluid intake
• D. To evaluate liver function

Answer: (A)

In diabetes insipidus, the kidneys lose the ability to concentrate urine, so patients dump large amounts of dilute urine. Without enough free water intake to match that loss, the serum sodium rises, leading to hypernatremia and high serum osmolality. This creates a dangerous environment for brain cells, and rapid or severe hypernatremia can provoke seizures. Therefore, monitoring serum sodium is essential to detect rising levels early and guide treatment to restore water balance and prevent neurologic complications. While kidney function, fluid intake, and liver function matter in overall care, none address the immediate risk that hypernatremia poses for seizures.