FLAER Based Assay According to Newer Guidelines Increases Sensitivity of PNH Clone Detection

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.

CD157 Can Replace CD24 and CD14 in a Single-Tube Flow-Cytometric Assay to Detect Paroxysmal Nocturnal Hemoglobinuria (PNH) Clones on Both Neutrophils and Monocytes: A Prospective Study From North India

Introduction

As per current guidelines, detection of paroxysmal nocturnal hematuria (PNH) clones on leucocytes requires the demonstration of the loss of at least two glycosyl-phosphatidyl-inositol (GPI)-linked molecules on both neutrophils and monocytes by flow cytometry. CD24 and CD14 are GPI-linked molecules expressed on neutrophils and monocytes respectively, whereas another GPI-linked molecule, CD157, is expressed on both neutrophils and monocytes. This prospective study evaluated the ability of CD157 to replace both CD24 and CD14 in a single-tube flow-cytometric assay to detect PNH clones on both neutrophils and monocytes.

Materials and methods

PNH clones were newly detected in 52 patients by an existing “standard” single-tube six-color flow-cytometric method, which was routinely performed in our laboratory at the time of undertaking this study. Six antibodies (CD45/CD15/CD64/CD24/CD14/FLAER) were used in this "standard" technique. Subjects were divided into two groups: (i) PNH disease (n=10), and (ii) aplastic anemia/myelodysplastic syndrome (AA/MDS) (n=42). Diagnosis of PNH disease and AA/MDS were made as per standard literature and guidelines. Results were compared with a single-tube five-color “test” assay using the antibodies CD45/CD15/CD64/CD157/FLAER by flow cytometry. Samples from 20 healthy control subjects were used to calculate cut-off values for the “test” assay.

Results

By the "test" method, cut-off values for detecting PNH clones obtained from receiver operating-characteristic curve analysis were >0.4% for neutrophils (sensitivity=96.15%, specificity=95%), and >0.9% for monocytes (sensitivity=98.08%, specificity=95%). There was significant correlation between PNH clone sizes measured by both the “standard” and “test” assays in neutrophils (PNH disease: r=0.976, p<0.001; AA/MDS: r=0.980, p<0.001) as well as monocytes (PNH disease: r=0.806, p=0.005; AA/MDS: r=0.915, p<0.001). Bland-Altman analysis showed agreement between both assays in all the 52 patients and in individuals with AA/MDS. The cost of the test to the patients was about 15% less in the “test” method than the ”standard” technique, with improved technical efficiency.

Conclusion

CD157 can replace both CD24 and CD14 in a single-tube flow-cytometric assay to detect PNH clones on both neutrophils and monocytes, with reduced cost to the patients and improved technical efficiency.