Simpler flame photometric determination of erythrocyte sodium and potassium: the reference range for apparently healthy adults.

Separated erythrocytes are washed repeatedly with iso-osmolar magnesium chloride solution, lysed by adding saponin, and sodium potassium measured in the diluted hemolysate by flame photometry. The coefficient of variation for the method was less than 4%. Reference intervals determined for a healthy population and hospitalized (elective surgery) patients without electrolyte disorders were 4.6-7.8 mmol/liter for erythrocyte sodium concentration and 94-110 mmol/liter for erythrocyte potassium concentration (2.5-97.5 percentiles).