Understanding the limitations of your assay using EQA data with serum creatinine as an example

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Analytical Toxicology

Background:

• Assay specificity and imprecision are critical for laboratory quality assessment.
• External Quality Assessment (EQA) materials require careful consideration of their composition.
• Serum matrix composition can influence EQA results and assay performance evaluation.

Purpose of the Study:

• To investigate the impact of serum matrix composition (single vs. pooled donors) on EQA results.
• To compare assay performance across multiple analytical methods using creatinine as a model analyte.
• To assess the influence of serum source on assay bias and variability in EQA.

Main Methods:

• Analysis of 36 specimens from 16 serum matrices (single and pooled donations) over 12 months.
• Inclusion of unmanipulated and creatinine-spiked serum.
• Evaluation of creatinine analysis data from approximately 500 UK laboratories using various methods.

Main Results:

• Only Roche Cobas and Siemens Atellica enzymatic creatinine assays met the 5.6% bias goal across all specimens.
• Pooled serum materials exhibited reduced bias variation across different analytical methods.
• Single donor serum showed greater variability in bias depending on the assay method.

Conclusions:

• Laboratories must understand assay limitations to avoid misinterpreting EQA/IQC data.
• EQA materials made from pooled donations can dilute interferents, potentially masking true assay bias.
• Careful selection of EQA material is essential for accurate assessment of laboratory assay performance and variability.