Mark Klimek Electrolytes and Endocrine Practice Test

Hypernatremia happens when there is a free-water deficit—water loss exceeds sodium loss, so the serum sodium concentration rises. Dehydration directly creates that deficit by reducing total body water without a proportional loss of sodium, whether through inadequate intake or losses like sweating, fever, or osmotic/insensible losses. That’s why dehydration is the best answer: it elevates the sodium concentration by removing water while leaving sodium relatively unchanged.

Edema and fluid overload involve excess body water and often dilute sodium, making hyponatremia or normal sodium more likely, not hypernatremia. Hyperkalemia is a potassium-related issue and does not inherently raise serum sodium.