Symptoms include polyuria, excessive thirst, and polydipsia, with a 24-h urine output of >50 mL/kg per day and a urine osmolality that is less than that of serum (<300 mosmol/kg; specific gravity <1.010). DI can be partial or complete; in the latter case the urine is maximally diluted (<100 mosmol/kg) and the daily urine output can reach 10-20 L. Clinical or laboratory signs of dehydration, including hypernatremia, occur only if the pt simultaneously has a thirst defect (not uncommon in pts with CNS disease) or does not have access to water. Other etiologies of hypernatremia are described in Chap. 1. Electrolytes/Acid-Base Balance.