Direct-measurement ion-selective electrodes: analytical error in hyponatremia.

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Biomedical Instrumentation

Background:

• Accurate sodium measurement is crucial for diagnosing and managing electrolyte imbalances.
• Direct ion-selective electrode (DISE) analyzers are widely used for sodium determination.
• Previous studies have indicated potential discrepancies in sodium measurements by different analytical methods.

Purpose of the Study:

• To evaluate the accuracy of commercial direct ion-selective electrode (DISE) analyzers for sodium measurement in hyponatremic samples.
• To compare DISE analyzer results with established methods like flame emission spectrophotometry (FES) and indirect ion-selective electrode (IISE) analyzers.
• To identify potential sources of error and propose solutions for improving sodium measurement accuracy.

Main Methods:

• Two commercial DISE analyzers were used to measure sodium concentrations in patient samples.
• Results from DISE analyzers were compared with those obtained from FES and IISE analyzers.
• Calibrant modification was explored as a method to correct observed discrepancies.

Main Results:

• DISE analyzers consistently yielded lower sodium values in hyponatremic cases compared to FES and IISE methods.
• The observed underestimation by DISE analyzers was attributed to issues with calibrant solutions.
• Modifying the calibrant was demonstrated to eliminate these measurement errors.

Conclusions:

• Commercial DISE analyzers require careful calibration and validation, especially for detecting hyponatremia.
• Standardized, internationally agreed-upon reference materials are needed for manufacturers and laboratories to ensure reliable analytical performance.
• Improvements in calibrants and reference standards are essential for accurate sodium determination using DISE technology.