A new method for determining plasma water content: application in pseudohyponatremia

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Biomedical Engineering

Background:

• Pseudohyponatremia results from elevated plasma protein or lipids, leading to artificially low measured sodium concentrations.
• Indirect ion-selective electrode (I-ISE) methods, common in labs, assume 93% plasma water and fail to correct for deviations, causing inaccurate sodium readings.
• Direct ion-selective electrode (D-ISE) methods measure sodium activity directly in plasma water, unaffected by protein or lipid levels.

Purpose of the Study:

• To introduce a novel quantitative method for determining plasma water content (PWC).
• To validate this method using both I-ISE and D-ISE techniques.
• To assess the utility of this method in analyzing dysnatremias.

Main Methods:

• Altering plasma water content in vitro by adding salt-free albumin to human plasma.
• Measuring plasma sodium concentration ([Na(+)](p)) using both I-ISE and D-ISE.
• Determining plasma water content (PWC) gravimetrically for comparison.
• Comparing gravimetrically determined PWC with PWC calculated from ISE measurements.

Main Results:

• Plasma water content (PWC) can be accurately determined by analyzing the difference in [Na(+)](p) measurements between I-ISE and D-ISE.
• The novel quantitative method demonstrated reliable PWC determination.
• The method shows potential as a valuable tool in diagnosing and managing dysnatremias.

Conclusions:

• A new method accurately quantifies plasma water content using standard laboratory equipment (I-ISE and D-ISE).
• This technique provides a reliable way to identify and analyze pseudohyponatremia.
• The method is a promising adjunct for the clinical analysis of electrolyte imbalances, specifically dysnatremias.