Effects of Hyperlipidemia on Plasma Sodium, Potassium, and Chloride Measurements by an Indirect Ion-Selective Electrode Measuring System

We used indirect ion-selective electrode (ISE) methods (Roche/Hitachi Modular) to investigate the effect of hyperlipidemia (cholesterol plus triglycerides) on measurements of sodium, potassium, and chloride and the ability of published formulas to correct for the decrease in measured Na+, K+, and Cl−. As recommended by Kroll (1), we did not use enriched samples but instead used 21 patient samples (lithium-heparin plasma and serum) with triglyceride concentrations >15 mmol/L, total lipid concentrations (cholesterol plus triglycerides; Roche/Hitachi Modular) >20 mmol/L, a lipemic index (Modular) >3, and a total protein concentration within the reference interval (62–83 g/L). We analyzed samples before and after ultracentrifugation (Airfuge; Beckman Coulter; 15 min at 107 000 g ) by indirect ISE potentiometry (Modular) and direct ISE (Rapidlab 865; Bayer). The ultracentrifuged indirect ISE result ( y ) and nonultracentrifuged direct ISE result ( z ) were subtracted from the nonultracentrifuged indirect ISE result ( x ; see Fig. 1 in the Data Supplement that appears with the online version of this letter at http://www.clinchem.org/content/vol52/issue1/). …