Pseudohyponatremia revisited: a modern-day pitfall.

Factitiously low sodium estimations are a hazard in most modern clinical laboratories. Most modern high-throughput analyzers use indirect ion-selective electrodes to estimate electrolyte concentrations in serum samples. This analysis is preceded by a dilution step of the sample. If the water concentration is altered by the presence of increased lipid or protein, the dilution step and the subsequent calculation of concentration by the analyzer results in a falsely low sodium value. This places patients at risk, particularly if the factitious result is acted upon by the physician. In this short review, we highlight this problem and review the methodology and situations where this artifact can occur and discuss strategies to circumvent this problem. When factitious results are suspected, whole blood sodium can be assessed using a direct ion-selective electrode, by measurement of osmolality, or by calculation of the serum water fraction and applying a correction to the reported value.