Spurious hyperchloremia and decreased anion gap in hyperlipidemia

A patient with overt lipemia presented with hyponatremia, hyperchloremia, and a negative anion gap. The hyperchloremia and negative gap resulted from overestimation of chloride levels due to a light-scattering effect in the colorimetric assay, an effect that was reproducible in vitro. In a prospective study, this effect produced substantial overestimations at even modest degrees of hyperlipemia. This effect expands the differential diagnosis of a decreased gap, adds to the list of technique-dependent artifacts in lipemia, and, if present, must be recognized for a patient's fluid and electrolyte status to be accurately defined.