A modified indirect method for determining erythrocyte sodium and potassium concentrations.

An automated method was adapted to measure the concentration of Na and K in plasma, nonhemolyzed whole blood, and hemolyzed whole blood, and thus allow the calculation of erythrocyte electrolyte con.centrations by a modified indirect method. The Na concentrations of nonhemolyzed whole blood and plasma were used to calculate the percent cell volume (hematocrit) of a blood sample. The percent cell volume and concentrations of Na and K in nonhemolyzed whole blood were used to modify the indirect method of calculating erythrocyte Na and K concentrations in canine, porcine, and human blood samples. Significant differences were found between the two indirect methods (indirect and modified indirect) used to calculate erythrocyte Na and K concentrations of human blood samples.