A client went to emergency room with a sudden onset of high fever and diaphoresis. Serum sodium was one of laboratory tests taken. Which of following values would you expect to see?

Correct Answer: B. 148 mEq/L.

The normal sodium level is 135-145 mEq/L. Diaphoresis and a high fever can lead to free water loss through the skin, resulting in increased sodium level (hypernatremia). Hypernatremia is defined as a serum sodium concentration of greater than 145 meq/l. The human body maintains sodium and water homeostasis by concentrating the urine secondary to the action of antidiuretic hormone (ADH) and increased fluid intake by a powerful thirst response.

• Option A: The basic mechanisms of hypernatremia are water deficit and excess solute. Total body water loss relative to solute loss is the most common reason for developing hypernatremia. Hypernatremia is usually associated with hypovolemia, which can occur in conditions that cause combined water and solute loss, where water loss is greater than sodium loss, or free water loss.
• Option C: Excessive sweating can occur due to exercise, fever, or high heat exposure. Renal losses can be seen in intrinsic renal disease, post-obstructive diuresis, and with the use of osmotic or loop diuretics. Hyperglycemia and mannitol are common causes of osmotic diuresis. Free water loss is seen with central or nephrogenic diabetes insipidus (DI) and also in conditions with increased insensible loss.
• Option D: Sodium excretion also involves regulatory mechanisms such as the renin-angiotensin-aldosterone systems. When serum sodium increases, the plasma osmolality increases which triggers the thirst response and ADH secretion, leading to renal water conservation and concentrated urine.