Mitigating electrolyte measurement discrepancies in high triglycerides samples: a comparative analysis of direct and indirect ISE for sodium, potassium and chloride measurements

Elevated triglyceride (TG) levels, common in hypertriglyceridemia, can significantly interfere with electrolyte analysis, particularly by the indirect ion-selective electrode (ISE) method. However, comprehensive data on the concentration-dependent measurement differences for potassium, sodium and chloride, along with validated corrective algorithms, are lacking. This study assessed the discrepancies in these electrolytes between direct and indirect ISE methods in serum samples with high TGs, while developing correction formulas for the indirect ISE. A total of 154 serum samples with high TGs and 50 control serum samples were analyzed in this retrospective cross-sectional study. Triglycerides were measured using colorimetric methods on the Roche Cobas 8000 analyzer (Roche Laboratories, Basel, Switzerland). Sodium, potassium and chloride were measured with direct ISE (Vitros 5600 Integrated System; Ortho-Clinical Diagnostics, Inc., Raritan, NJ) and indirect ISE (Roche Cobas 8000 analyzer). Our results revealed significant negative biases in the indirect ISE, particularly in samples with TG >20.00 mmol/L. For TG levels between 20.01 and 30.00 mmol/L, the negative biases for sodium, potassium and chloride were -2.31%, -3.86% and -4.58%, respectively. Notably, in the subgroup with TG >60.00 mmol/L, the negative biases reached their maximum values: -12.05% for potassium, -6.88% for sodium, and -10.59% for chloride. Additionally, linear correction formulas that aligned indirect results with direct measurements were developed and validated. Post-correction, differences fell within clinical thresholds (Diff_Na of |4| mmol/L, Diff_Cl of |4| mmol/L, Diff_K of |0.5| mmol/L). Collectively, high TGs impact electrolyte measurements by indirect ISE, but the correction formulas might mitigate the discrepancies. These correction formulas were platform-specific, and their generalizability to other analytical systems requires further investigation.