Standardisation, calibration and development of novel flow cytometry techniques
Bead count rate (BCR) monitoring successfully identifies pipetting error during single platform enumeration. Enumeration beads are a stable constant in each patient’s sample and if these can be multitasked to monitor overall flow cytometer operation in a model of continuous quality control (CQC), they could reveal further details of flow cytometer operation and fulfill more quality assurance functions than identify pipetting error alone. Methods The CQC model used manufacturer recommended quality control procedures daily. In addition, methods were developed to monitor flow cytometer fluidics and electronics as well as sample preparation to standardise and extended quality monitoring. Sample-to-sample CQC included monitoring BCR, selected time, optical and fluorescence histograms as well as FPCV and MCN. This model also incorporated diligent monitoring of BCR patterns to detect instrument malfunctions. Post standardisation and implementation of the CQC model, an extended EQA exercise assessed bias between standardised CD4 counting methods and determined a ‘near true’ CD4 count to use as a calibrator. Conclusion The proposed CQC model standardised overall flow cytometer and automated sample preparation systems and, established imprecision reference intervals for each aspect of testing (fluidics <3%, sample preparation 2-4% and protocol and electronics <2%). Further BCR pattern recognition was used to identify instrument malfunctions in real-time and, longitudinally for pro-actively identifying imminent breakdowns. CD4 counts were calibrated to consensus mean ‘near true’ counts on two flow cytometers in the Reference Laboratory.