Which option correctly pairs the type of hypotonic hyponatremia with an example?

• A. Hypovolemic hyponatremia - GI losses, excessive sweating
• B. Hypovolemic hyponatremia - GI losses, SIADH
• C. Isovolemic hyponatremia - CHF
• D. Hypervolemic hyponatremia - renal failure

Answer: (A)

In hyponatremia due to low serum osmolality, the patient’s volume status helps reveal the mechanism. Hypovolemic hyponatremia arises when there is a loss of extracellular fluid that includes sodium, such as from GI losses or excessive sweating. This fluid loss decreases effective circulating volume, and the body compensates by releasing ADH to conserve water. The net effect is water retention that dilutes serum sodium, producing hyponatremia. GI losses and sweating are classic triggers of this pattern, making them the best example of hypovolemic hyponatremia.

Other scenarios illustrate different volume states: SIADH usually causes euvolemic hyponatremia because total body water increases without true volume depletion; CHF and renal failure typically lead to hypervolemic hyponatremia with fluid overload.