.... Hyponatremia Inappropriate ADH syndrome Urea Hyponatremia, defined as a plasma sodium (PNa) concentration <135 mmol/L, is the most common electrolyte disorder encountered clinically. Hyponatremia is categorized as mild (i.e., PNa 130–134 mmol/L), moderate (i.e., PNa 120–129 mmol/L), or severe (i.e...