FLAER as a standalone reagent for paroxysmal nocturnal hemoglobinuria: Do we need to reconsider the guidelines for testing?

Introduction: Flow cytometry‐based paroxysmal nocturnal hemoglobinuria (PNH) testing involves utilization of monoclonal antibodies against GPI‐linked proteins and FLAER. The ability of FLAER to bind to a wide variety of GPI‐linked structures and to be utilized across different leukocyte subsets is remarkable. We hypothesize that FLAER as a standalone reagent may be equally effective for detecting PNH clones. The present study intends to compare the results of a FLAER alone‐based strategy to the recommended FLAER+GPI‐linked protein‐based approach for applicability in clinical settings. Methods: EDTA‐anticoagulated blood samples from patients for PNH workup were tested for PNH by multiparametric flow cytometry. A conventional panel comprising gating markers (CD45 for WBC, CD15 for granulocytes, and CD64 for monocytes) and a combination of FLAER and GPI‐linked markers, such as CD24 and CD14, henceforth referred to as the "routine panel," was employed. Second, a "FLAER‐only panel" comprising the gating markers and FLAER alone (excluding the GPI‐linked markers CD24 and CD14) was set up. The samples were processed using the lyse‐wash‐stain‐wash technique, and events were acquired on BC Navios Ex flow cytometer (Beckman Coulter, Inc., USA) and analyzed on Kaluza Software 2.1. The presence of a PNH clone was reported at a value of ≥0.01%. Results: A total of 209 patients were tested. Both panels found a PNH clone in 20.1% of patients (n = 42/209) with a 100% concordance rate. The PNH clone range for granulocytes was 0.01%–89.68%, and for monocyte was 0.04%–96.09% in the routine panel. The range in the FLAER‐only panel for granulocytes was 0.01%–89.61%, and for monocytes, it was 0.01%–96.05%. Pearson correlation statistics revealed a significant correlation between the size of the PNH clone of granulocytes and monocytes among the two panels tested (granulocytes r = 0.9999, p < 0.0001, 95% CI = 0.9999 to 1.000; monocytes r = 0.9974, p < 0.0001, 95% CI = 0.9966–0.9980). Conclusion: Based on our results, FLAER as a standalone marker is specific and sensitive for identifying PNH clones in granulocytes and monocytes, even for high‐sensitivity PNH assay. The proposed "FLAER‐only panel" panel is efficient and cost‐effective for highly sensitive PNH testing in two different cell lineages, especially in resource‐limited clinical settings. [ABSTRACT FROM AUTHOR]