The between-run component of variation in internal quality control

Area of Science:

• Laboratory Medicine
• Statistical Process Control
• Analytical Chemistry

Background:

• Imprecision in laboratory assays often stems from between-run variation, particularly in immunoassay methods.
• Effective quality control is essential for reliable analytical results.

Purpose of the Study:

• To design and outline control charts for monitoring the mean, within-run variance, and between-run variance components.
• To emphasize the importance of controlling between-run variation for assay precision.

Main Methods:

• Development of control charts for key statistical measures of assay performance.
• Presentation of power curves to illustrate chart performance under various conditions.
• Analysis of the impact of between-run variation on the power to detect systematic errors.

Main Results:

• Control charts for mean, within-run variance, and the ratio of between-run to within-run variance are presented.
• Between-run variation significantly impacts the ability to detect systematic errors, setting an upper limit on achievable power.
• When between-run variation dominates, limiting controls to approximately four per run is advisable.

Conclusions:

• Explicit control of between-run variation is vital for analytes measured by immunoassay principles.
• The presence of between-run variation inherently limits the sensitivity to systematic errors.
• Optimal quality control strategies must account for the relative contributions of within-run and between-run variation.