A multilaboratory-evaluated reference method for the determination of serum sodium

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Accurate serum sodium measurement is critical for diagnosing and managing various medical conditions.
• Existing methods may lack the precision and accuracy required for a definitive Reference Method.
• Flame atomic emission spectroscopy (FAES) offers potential for precise elemental analysis.

Purpose of the Study:

• To evaluate a flame atomic emission spectroscopic (FAES) method for serum sodium determination.
• To establish FAES as a validated Reference Method for serum sodium analysis.
• To assess the method's performance against predefined criteria for imprecision and bias.

Main Methods:

• A statistically designed, multilaboratory study was conducted.
• Serum pools with sodium concentrations ranging from 110-160 mmol/L were analyzed.
• Definitive sodium values were determined by ion-exchange/gravimetry at the National Bureau of Standards.
• FAES results were compared against performance criteria: maximum imprecision of 1.5 mmol/L and maximum bias of 2.0 mmol/L.
• Both manual and semi-automated pipetting techniques were evaluated.

Main Results:

• The FAES method satisfied the predefined performance criteria for a Reference Method.
• The standard error of a single laboratory's performance ranged from 0.46 to 0.86 mmol/L.
• The maximum bias observed was 1.0 mmol/L, well within the acceptable limit.
• Both manual and semi-automated pipetting modes met acceptability criteria.
• Semi-automated pipetting was selected for the final Reference Method description.
• Fewer than four replicate analyses were sufficient to meet precision criteria.

Conclusions:

• The evaluated flame atomic emission spectroscopic (FAES) method is suitable as a Reference Method for serum sodium.
• The method demonstrates high precision and low bias, ensuring reliable sodium measurements.
• Semi-automated pipetting is recommended for optimal performance and reproducibility.
• The study confirms the utility of FAES in achieving accurate and precise clinical chemistry diagnostics.