Sodium determination by indirect ion selective electrode is falsely decreased by which condition?

Sodium determination by indirect ion selective electrode is falsely decreased by which condition?

• A. Elevated chloride levels
• B. Elevated lipid levels
• C. Decreased protein levels
• D. Decreased albumin levels

Answer: (B)

Indirect ISE sodium measurement dilutes the plasma and assumes a normal plasma water fraction. When lipids are elevated, the nonaqueous (lipid-rich) portion of plasma increases, reducing the fraction of plasma that is water. Because the assay analyzes the diluted aqueous phase, the sodium concentration appears lower than it truly is—pseudo-hyponatremia. Direct ISE doesn’t rely on a dilution step and is less affected by this nonaqueous fraction, so it won’t show the same artificial fall. Thus, elevated lipid levels cause a falsely decreased sodium result with indirect ISE.

Indirect ISE sodium measurement dilutes the plasma and assumes a normal plasma water fraction. When lipids are elevated, the nonaqueous (lipid-rich) portion of plasma increases, reducing the fraction of plasma that is water. Because the assay analyzes the diluted aqueous phase, the sodium concentration appears lower than it truly is—pseudo-hyponatremia. Direct ISE doesn’t rely on a dilution step and is less affected by this nonaqueous fraction, so it won’t show the same artificial fall. Thus, elevated lipid levels cause a falsely decreased sodium result with indirect ISE.