Quantifying interpretive contributions to analytical variability in clinical flow cytometry.

Area of Science:

• Clinical diagnostics
• Immunophenotyping
• Analytical chemistry

Background:

• Reproducibility in clinical flow cytometry is critical for accurate patient diagnosis and monitoring.
• Standardization efforts have minimized technical variability, but human interpretation during manual gating remains a significant source of error.
• Threshold-based lymphocyte measurements, like absolute CD4 counts, are vital for clinical management and require high precision.

Purpose of the Study:

• To quantify the variability introduced by human interpretation in routine clinical TBNK flow cytometry.
• To assess the impact of interpretive variability on CD4 decision-band classification.
• To establish a reference for analytical performance and evaluate deviations under routine conditions.

Main Methods:

• A two-stage workflow audit using a fixed, automated analysis as a reference standard.
• Analysis of standardized quality-control materials and 320 clinical samples by six technologists on three harmonized cytometers.
• Definition of an empirical analytical performance envelope to evaluate routine testing deviations.

Main Results:

• Under quality control, automated-manual differences were minimal and interpretable, with preserved CD4 classification.
• Routine clinical samples exhibited significant variability, primarily driven by operator identity, not instrument differences.
• Operator-associated variability was concentrated near CD4 thresholds, leading to discordant classifications.

Conclusions:

• Human interpretation in manual gating is a significant, previously unquantified source of analytical variability in clinical flow cytometry.
• This interpretive variability can impact threshold-based clinical classifications, such as CD4 counts, despite acceptable quality control.
• Addressing operator variability is crucial for improving the reliability of flow cytometry results in clinical decision-making.