Pseudohyponatremia revisited: a modern-day pitfall

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Analytical Chemistry

Background:

• Modern clinical laboratories frequently use indirect ion-selective electrodes for electrolyte analysis.
• These analyzers perform sample dilution before concentration calculation.
• Altered serum composition (lipids, proteins) can interfere with this dilution process.

Purpose of the Study:

• To highlight the hazard of factitiously low sodium estimations.
• To review the methodology and situations leading to this artifact.
• To discuss strategies for circumventing falsely low sodium values.

Main Methods:

• Review of analytical methodologies for electrolyte determination.
• Analysis of interference from sample matrix variations (lipids, proteins).
• Discussion of alternative sodium measurement techniques.

Main Results:

• Indirect ion-selective electrode methods can yield falsely low sodium values when sample water content is altered.
• This artifact arises from the dilution and calculation steps in high-throughput analyzers.
• Physician action based on erroneous results poses a patient risk.

Conclusions:

• Factitious low sodium estimations are a significant clinical laboratory hazard.
• Understanding sample composition interferences is crucial for accurate results.
• Strategies like direct ion-selective electrode measurement or osmolality assessment can verify sodium levels.