Inter-laboratory validation of a harmonized PNH flow cytometry assay

BACKGROUND A network comprising 11 laboratories aimed to consolidate PNH testing by developing and validating an assay guided by previous guidelines and studies. Network analyses of >20 native samples yielded key findings that were used to create and reshape the final protocol. METHODS Twenty-seven native samples were distributed to all participating laboratories for blind testing, local analysis, and subsequent re-analysis by a central laboratory. Inter-laboratory clone size precision (coefficient of variation [CV]) was monitored for each sample, and the findings used to refine the test protocol. Linearity and precision tests were performed, assay limits of blank and detection were calculated, and limits of quantification were determined. RESULTS When using the final protocol, enumeration of cells with a PNH phenotype by all participating laboratories was comparable, with no clinically significant discrepancies or false-positive or false-negative results reported. Of note, the biological characteristics of the sample affected precision. For example, CVs were higher when PNH and normal cells showed contiguous expression of GPI-linked antigens. A red cell gating strategy that eliminated non-specific type II PNH phenotypic events was devised, enabling reliable reporting of events in the type II red cell gate. The final protocol provided an assay with a Limit of Quantification of 0.01% for neutrophils and red cells, and 0.1% for monocytes. CONCLUSIONS We describe a robust network-validated PNH assay that may aid other laboratories to set up and validate high resolution PNH analysis. © 2018 International Clinical Cytometry Society.