A Gradual Positive Bias in Chloride Measurements with a Major Automated Chemistry Platform

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Analytical Chemistry

Background:

• Chloride, an extracellular anion, is typically measured using ion-selective electrode (ISE) methods.
• Routine quality control and proficiency testing failed to detect a gradual positive bias in chloride measurements on the Siemens Healthineers Atellica CH platform.

Purpose of the Study:

• To investigate and characterize a subtle positive bias in chloride measurements using the Siemens Healthineers Atellica CH platform.
• To evaluate the effectiveness of standard quality control measures in detecting assay drift for routine analytes.

Main Methods:

• Retrospective analysis of laboratory values from healthy outpatients (ICD-10 code Z00.00) from 2017-2024.
• Reference interval verification, comparison with peer group means from proficiency testing surveys (College of American Pathologists), and method comparison studies with an alternate platform.

Main Results:

• Patient data analysis (2017-2024) showed a gradual increase in median chloride concentrations, unlike other electrolytes.
• In 2024, 64.3% of chloride results exceeded the reference interval, despite successful verification in 2021.
• Proficiency testing revealed a mean positive bias of 3.19 mmol/L compared to other indirect ISE methods (2019-2024), and method comparison showed a +4.3 mmol/L bias.

Conclusions:

• Peer group targets in quality control and proficiency testing masked the gradual drift in chloride measurements.
• Utilizing aggregate patient data with specific diagnostic codes (ICD-10) is a valuable method for detecting assay performance issues.
• Continuous monitoring of routine analyte assay performance is crucial to prevent potential adverse effects on patient care.