Pseudohyponatremia.

Pseudohyponatremia should be distinguished from true hyponatremia lest injudicious therapy be instituted. Pseudohyponatremia is caused by a displacement of serum water by elevated concentrations of serum lipids or proteins. Only two (flame photometry and indirect potentiometry) of the three current methods available for measuring serum sodium involve sample dilution and may consequently produce spuriously low sodium values. The third method (direct potentiometry) involves no sample dilution, and sodium measurements are unaffected by hyperlipidemia and hyperproteinemia. As all three methods for sodium measurements may coexist in a clinical laboratory, it is important for the physician to be aware not only of the serum value but also the method employed.