Ketonuria contributes to hyponatremia by which mechanism?

• A. Increased sodium loss via excretion
• B. Decreased water intake
• C. Increased water retention
• D. Measurement artifact

Answer: (A)

Ketonuria causes osmotic diuresis. The ketone bodies in the urine pull water into the tubular fluid and drive more urine production, along with the loss of solutes such as sodium. As sodium is excreted in greater amounts in the urine, serum sodium falls, leading to hyponatremia. This mechanism is consistent with the observed electrolyte disturbance, whereas decreased water intake or increased water retention would not primarily explain the sodium loss seen with ketone-driven diuresis, and measurement artifact is unlikely.