Serum lithium. A CAP survey perspective

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Laboratory Medicine

Background:

• Accurate lithium measurement is crucial for therapeutic drug monitoring.
• Interferences in analytical methods can affect patient treatment.
• Standardization of laboratory assays is essential for reliable results.

Purpose of the Study:

• To analyze lithium measurement methods from the 1975 College of American Pathologists Comprehensive Chemistry Survey.
• To identify and compare biases between different analytical techniques for lithium determination.
• To investigate potential causes for observed discrepancies in lithium measurements.

Main Methods:

• Analysis of lithium data categorized by method: flame emission spectrophotometry and atomic absorption spectrophotometry.
• Correlation of method bias with sample mean.
• Comparison of results using three paired specimens.

Main Results:

• Atomic absorption methods demonstrated a negative bias relative to flame emission methods.
• A correlation between bias and sample mean suggests potential standardization errors.
• Protein depression effects and viscosity differences between standards and samples were hypothesized as contributing factors.

Conclusions:

• Atomic absorption methods may be subject to standardization errors impacting lithium measurements.
• Differences in sample matrix (serum vs. aqueous standards) could influence accuracy.
• Both flame emission and atomic absorption methods provided clinically acceptable variability in 1975.