Pseudohyponatremia in multiple myeloma.

Severe hyponatremia in any asymptomatic patient should alert the clinician to the possibility that pseudohyponatremia may be attendant with chylomicronemia or paraproteinemia. In cases of chylomicronemia, the serum is creamy, and in paraproteinemia the serum has increased viscosity. In such cases, the calculated serum osmolality will be decreased but the measured value will be within the normal range. Hyponatremia in an asymptomatic patient demands careful evaluation before institution of therapy. In addition, the presence of a normal serum sodium level in a patient with multiple myeloma should alert the clinician to the possibility that hypernatremia and hypertonicity may be present.