Cushing's disease is listed as an additional cause of hypernatremia. Which of the following is another listed cause?

• A. Severe dehydration
• B. Acute diarrhea
• C. Hyperaldosteronism
• D. Addison's disease

Answer: (A)

Hypernatremia happens when there is more sodium relative to water in the body, i.e., a free-water deficit. When a person loses a lot of body water or doesn’t replace it adequately, the concentration of sodium in the blood rises even if total body sodium is unchanged.

Severe dehydration directly creates that water deficit. Substantial water loss can occur from sweating, fever, vomiting, diarrhea, or inadequate fluid intake. If water loss isn’t matched by drinking enough fluids, the plasma becomes more concentrated, raising the sodium level.

Other options are less likely as the primary cause in this context. Addison’s disease tends to cause hyponatremia rather than hypernatremia due to cortisol deficiency and its effects on water balance. Acute diarrhea can contribute to electrolyte disturbances, but it does not consistently produce hypernatremia as reliably as a simple, substantial loss of water does. Hyperaldosteronism can raise sodium, but the classic and most direct cause among the listed factors is severe dehydration.