Assessment of EQA reference conventional flow cytometers for clinical CD4+ T-cell enumeration

Background CD4 + T-cell enumeration continues to be an essential marker for assessing immunodeficiency and monitoring HIV disease progression. Enrollment in an external quality assessment (EQA) program is a strong tool for diagnostics as it allows for identification and correction of potential errors that may occur during testing. The aim of this article is to investigate the effect of our repeated participation in an EQA program on the performance of our internal flow cytometry instruments, namely the Navios and FACSCalibur, as an EQA provider. Methods We compiled data from 14 Canadian Immunology Quality Assurance Program (CIQAP) EQA sessions and compared the Navios and FACSCalibur results to the aggregate group mean (AGM) of each session. The standard deviation index (SDI), residual, and percent differential was performed to identify trends in data and identify any potential problems. A Bland-Altman analysis was performed comparing both of these flow cytometry instruments. Results Our results showed good performance overall with trend variation between the relative (%) and absolute count CD4 + T-cell results for both of the instruments. We observed a good agreement between instruments and identified that all HIV+ samples with low relative CD4 + T-cell results (< 28%) were overestimated by Navios compared to FACSCalibur. Conclusion As an EQA coordinator, using the same instruments as participating laboratories allows more accurate monitoring of instrument performance and variability, supporting a stronger analysis of corrective action based on participant results.