Pseudohyponatremia in idiopathic nephrotic syndrome with severe edema is attributed to hyperlipidemia that results in displacement of a portion of water phase of plasma. Current methods of measurement of serum electrolytes are unaffected by hyperlipidemia. In this report we demonstrate that patients with idiopathic nephrotic syndrome with severe edema and true hyponatremia may have an increased rather than normal osmolal gap. We believe that this could be secondary to non-Na+ and non-K+ osmoles in response to plasma-volume contraction secondary to hypoalbuminemia. This observation has implications for management of severe edema in such patients, because fluid restriction could increase their risk for pre–renal failure.

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