Practical guidelines for the high-sensitivity detection and monitoring of paroxysmal nocturnal hemoglobinuria clones by flow cytometry

Diagnostic landscape of first-time cytometric screening for paroxysmal nocturnal hemoglobinuria in Poland in 2013-2022

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hematopoietic stem cell disorder characterized by PIG-A mutations, leading to glycophosphatidylinositol (GPI)-anchored proteins deficiency that triggers hemolysis - a hallmark of the disease. PNH diagnostics is based on high-sensitivity multicolor flow cytometry (MFC), enabling to detect even small populations of PNH cells. In this single-center, retrospective study, we aimed to characterize a cohort of PNH clone-positive patients first time screened from January 1st, 2013 until December 31st, 2022 with MFC according to International Clinical Cytometry Society PNH Consensus Guidelines.

RESULTS

Out of 2790 first-time screened individuals, the presence of PNH clone in neutrophils was detected in 322 patients, including 49 children and 273 adults. Annual incidence was stable at a median of 31 patients (14 and 19 with clone sizes ≤ 1% and > 1%, respectively), with a decline in number of patients with clone sizes > 1% observed in 2020, potentially influenced by the COVID-19 pandemic. The most common screening indications were aplastic anemia and other cytopenias.

CONCLUSIONS

A significant underrepresentation of hemolytic patients was observed as compared to the published cohorts suggesting that these patients are missed in diagnostic process and classic PNH remains underdiagnosed in Poland.

European flow cytometry quality assurance guidelines for the diagnosis of primary immune deficiencies and assessment of immune reconstitution following B cell depletion therapies and transplantation

Over the last 15 years activity of diagnostic flow cytometry services have evolved from monitoring of CD4 T cell subsets in HIV-1 infection to screening for primary and secondary immune deficiencies syndromes and assessment of immune constitution following B cell depleting therapy and transplantation. Changes in laboratory activity in high income countries have been driven by initiation of anti-retroviral therapy (ART) in HIV-1 regardless of CD4 T cell counts, increasing recognition of primary immune deficiency syndromes and the wider application of B cell depleting therapy and transplantation in clinical practice. Laboratories should use their experience in standardization and quality assurance of CD4 T cell counting in HIV-1 infection to provide immune monitoring services to patients with primary and secondary immune deficiencies. Assessment of immune reconstitution post B cell depleting agents and transplantation can also draw on the expertise acquired by flow cytometry laboratories for detection of CD34 stem cell and assessment of MRD in hematological malignancies. This guideline provides recommendations for clinical laboratories on providing flow cytometry services in screening for immune deficiencies and its emerging role immune reconstitution after B cell targeting therapies and transplantation.

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.

COVID-19 vaccination prevents a more severe course and treatment with complement inhibitors reduce worsening hemolysis during the Omicron pandemic in patients with PNH: a single-center study

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disease characterized by chronic complement-mediated hemolysis. The concentrated outbreak of coronavirus disease 2019 (COVID-19) in China after 6 December 2022, provided an opportunity to observe the disease course of PNH during an active Omicron infection epidemic.

PATIENTS AND METHOD

Patients diagnosed with PNH at Peking Union Medical College Hospital (PUMCH) before 6 December 2022, were followed up until 10 April 2023. Clinical data related to coronavirus infection and hemolysis were recorded. Factors influencing the infection and severity rate of Omicron, as well as hemolysis provocation, were analyzed.

RESULTS

In total, 131 patients with PNH were included in this retrospective analysis; 87.8% were infected with Omicron. Among them, 15.7% met the criteria for severity, and 1 patient died (0.87%). No protective factors were identified against Omicron infections. However, patients with severe Omicron infection (n = 18) had a lower vaccination rate than those with non-severe infection (n = 97; p = 0.015). Among those infected (n = 115) with Omicron, there was a significant increase in lactate dehydrogenase (LDH) levels compared with those in the uninfected group (n = 16, p = 0.000). Patients with severe infections (n = 18) had even higher LDH increase rates than those without severe infections (n = 97; p = 0.002). 10 (37.0%) patients treated with complement inhibitors developed breakthrough hemolysis (BTH). Patients treated with complement inhibitors (n = 27) exhibited less severe hemolysis than treatment-naïve patients (n = 104; p = 0.003).

CONCLUSIONS

Omicron infection exacerbates hemolytic attacks in patients with PNH. Vaccination helps mitigate the severity of Omicron infection, and using complement inhibitors reduces hemolysis exacerbation.

Summary of validation considerations with real-life examples using both qualitative and semiquantitative flow cytometry assays

In the clinical laboratory, flow cytometry assays are critical to providing diagnostic and prognostic information to the treating clinicians. A validation or verification provides confidence that the assay will yield reliable results that can be trusted to make critical medical decisions. The following performance specifications should be included in a validation for laboratory developed tests as needed: accuracy (or trueness), precision (reproducibility and repeatability), detection capability, selectivity, reference range, and sample and reagent stability. We define these terms and present our approach to validation of several common flow cytometry assays, including examples of a leukemia/lymphoma assay and a paroxysmal nocturnal hemoglobinuria (PNH) assay.

Clinicopathological Profile of Paroxysmal Nocturnal Hemoglobinuria among Omani Patients: A Case Series

We aimed to estimate the nature and prevalence of paroxysmal nocturnal hemoglobinuria (PNH) among Omani patients. We performed a retrospective review of all patients who were tested for PNH by flow cytometry at the Sultan Qaboos University Hospital, Muscat, between 2012 and 2019. Manifestations, treatment modalities, and outcomes were assessed. A total of 10 patients were diagnosed or were on follow-up for PNH (median age 22.5 years). Clinical manifestations included fatigue (80%) and anemia (70%). Six patients had classical PNH with hemolysis, three had PNH in the context of aplastic anemia, and one patient had subclinical PNH. The median total clone size (type II + III) for neutrophils was 95.5 (range: 1.5-97) (FLAER/CD24) and for monocytes was 91.6 (range = 0.04-99) (FLAER/CD14). Four patients had clone sizes > 50% at the time of diagnosis. The median follow-up period of the patients was 62 months (range = 8-204 months). One patient suffered thrombosis. Three patients were on immunosuppressant agents, five were initiated on eculizumab, and four had a bone marrow transplant. No deaths were reported in the cohort. The estimated average incidence of PNH among Omani patients was 1.5 per 5 000 000. PNH is rare in the Omani population. The predominant presentation is hemolytic anemia.

Validation of a single tube 3-colour immature red blood cell screening assay for the detection and enumeration of small, medium and large paroxysmal nocturnal haemoglobinuria clones by flow cytometry

INTRODUCTION

The reliable diagnosis of paroxysmal nocturnal haemoglobinuria (PNH) by flow cytometry is based on mandatory analysis of the erythroid, neutrophilic and monocytic lineages. In this study, we have evaluated the performance characteristics of a recently published immature red blood cell (iRBC) assay as a potential screening test for PNH by flow cytometry.

METHODS

Intra- and inter-assay imprecision were determined in five replicates of small, medium and large PNH iRBC clones. Analytical and functional sensitivity was assessed by performing spiking tests for five replicates. Thirty healthy donors and 441 PNH patients were tested for evaluation of clinical specificity, sensitivity, positive and negative predictive values.

RESULTS

Coefficients of variation (CV) for intra-/inter-assay imprecision analyses were 1.31/1.50, 3.19/2.61 and 3.99/1.58 for the big, medium and small clone sizes, respectively. Absolute values (100%) were found for both clinical specificity and sensitivity as well as for both positive and negative predictive values. The CV from 5 replicate results for 10 clustered events was 15.7%. The coefficient of determination (r² ), Pearson's correlation coefficient (r) and Bland-Altman mean bias were 0.9436/0.9234/1.7 for PNH iRBC compared to PNH neutrophils and 0.9553/0.9387/2.1 for PNH iRBCs compared to PNH monocytes.

CONCLUSION

Our results confirm very good performance characteristics, high analytical and functional sensitivity, absolute clinical specificity and sensitivity as well as favourable correlation between PNH iRBCs and both PNH neutrophils and monocytes, suggesting that this cost-effective 3-colour iRBC assay can be used as a reliable screening test for evaluation of small, medium and large PNH clones by flow cytometry.

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.

Frequencies of glycosylphosphatidylinositol (GPI)-deficient cells using high-sensitivity flow cytometry as per the 2018 ICCS/ESCCA consensus guideline in patients with hematologic malignancy, aplastic anemia, or cytopenia

OBJECTIVES

We examined the frequencies and sizes of glycosylphosphatidylinositol(GPI)-deficient cells as per the International Clinical Cytometry Society/European Society for Clinical Cell Analysis(ICCS/ESCCA) consensus guidelines for the high-sensitivity detection of GPI-deficient cells.

METHODS

In 2018, the ICCS/ESCCA guidelines for the high-sensitivity detection of GPI-deficient cells were published. We evaluated frequencies and sizes of GPI-deficient red blood cells(RBCs), neutrophils, and monocytes as determined using the ICCS/ESCCA guidelines and Clinical and Laboratory Standards Institute(CLSI) guidelines in patients with a hematologic malignancy, aplastic anemia, or cytopenia.

RESULTS

A total of 106(38.7%) patients exhibited GPI deficiency in at least one blood cell lineage. GPI-deficient cells of one or more lineages were found in 62.7% of patients with a hematologic malignancy, 51.1% of patients with aplastic anemia, and 23.4% of patients with cytopenia. GPI-deficient monocytes were most frequently detected in all three groups. By population size, GPI-deficient clones (>1%) in monocytes were mostly detected in patients with a hematologic malignancy or aplastic anemia. Rare cells with GPI deficiency(<0.1%) in monocytes were most common among patients with cytopenia.

CONCLUSION

High-sensitive flow cytometry analysis including monocytes may be necessary for patients with a hematologic disorder.

Current Opinions on the Clinical Utility of Ravulizumab for the Treatment of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder of hematopoietic stem cells genetically defined by the acquisition of somatic mutations in the X-linked phosphatidylinositol glycan anchor biosynthesis, class A (PIGA) gene. PIGA is essential for the synthesis of glycosyl phosphatidylinositol (GPI) anchor proteins and its mutations result in a deficiency of such molecules on the membrane of blood cells derived from the mutant clone. In particular, the lack of the GPI-linked complement regulatory proteins CD55 and CD59 is responsible for the increased sensitivity of PNH erythrocytes to complement-mediated destruction. Indeed, the classical clinical picture of PNH includes signs and symptoms of intravascular hemolysis along with variable degrees of cytopenia and a strong tendency to thrombosis, hallmarks of the disease. Before the introduction of anti-complement inhibitors, PNH was characterized by a high mortality primarily due to thrombotic events. The approval of the terminal anti-complement inhibitor eculizumab in 2007 introduced a paradigm shift in the treatment of the disease with improvement of the chronic hemolytic process and dramatic reduction of the thrombotic rate. However, eculizumab has a relatively short half-life when considering a life-long treatment, with obvious consequences as to the quality of life of treated patients necessitating relatively frequent drug administrations. Moreover, up to 30% of PNH patients undergoing eculizumab therapy show a suboptimal response, continuing to require red cell transfusions because of extravascular hemolysis or breakthrough hemolytic episodes. In 2019, the FDA approved the second-generation C5 inhibitor ravulizumab, a long-lasting agent with a better control of disease manifestations. Herein, we discuss the use of ravulizumab in PNH, its differences with first-generation C5 inhibitors, the research evidence supporting the safety and efficacy of this drug and its impact on costs for health systems and quality of life of PNH patients.

COVID19 infection in a patient with paroxysmal nocturnal hemoglobinuria: A case report

INTRODUCTION

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired, life-threatening hemopoietic stem cell disorder characterized by the triad of hemolytic anemia, thrombosis, and impaired bone marrow function. Evidence suggests that severe outcomes in COVID19 infection are attributed to the excessive activation of the complement cascade leading to acute lung injury and associated is with an increased prothrombotic state.

PATIENT CONCERNS

A 27-year-old Caucasian man with PNH presented to the Emergency Department of our hospital with acute onset shortness of breath, cough and blood in urine.

DIAGNOSIS

The patient was diagnosed with acute hemolytic exacerbation of PNH complicated with moderate COVID19 pneumonia.

OUTCOMES

The patient was initiated with an anticoagulant unfractionated heparin, dexamethasone, and cefuroxime injection. His symptoms quickly resolved, and he was discharged after 5 days.

CONCLUSION

The complement system activation is a critical component in the sequalae of COVID19 infection. Evidence suggests that severe outcomes in COVID19 infection are attributed to the excessive activation of the complement cascade leading to acute lung injury and associated is with an increased prothrombotic state. Notably, C5a concentration was noted to be higher in patients with COVID19 infection. The use of complement inhibitors to attenuate immune mediated damage in COVID19 nevertheless represents a very interesting theoretical approach. However, careful consideration as to which patients may benefit will be required and the outcome of clinical trials needed.

JAK2V617F positive polycythemia vera with paroxysmal nocturnal hemoglobinuria and visceral thromboses: a case report and review of the literature

Background

Polycythemia vera (PV) is characterized by red cell mass expansion in the peripheral blood and can be complicated with thrombosis, bleeding, evolution to acute myeloid leukemia (AML) or a fibrotic phase. Paroxysmal nocturnal hemoglobinuria (PNH) in an acquired clonal haematopoietic stem cell disorder associated with chronic intravascular hemolysis, venous thrombosis, defective hematopoiesis, frequent episodes of infection and, rarely, leukemic transformation. Herein, we report an interesting case of a patient with coexistence of PNH clones and a JAK2V617F positive PV, with unusual thromboses without hemolysis.

Case presentation

A 51-year-old woman presented with increased levels of hematocrit, multiple liver, spleen, and left kidney infarctions and ascites; further investigation revealed a JAK2V617F-positive polycythemia vera and the presence of a significant PNH population (more than 90% CD55– CD59– cells among both granulocytes and red blood cells). Interestingly, the patient has experienced severe thrombotic events without any signs or symptoms of hemolysis.

Conclusions

This case raises questions over uncharted aspects of the PNH etiopathogenesis and its potential association with myeloproliferative neoplasms (MPN) and highlights the difficulty of diagnosing and managing patients with more than one potentially thrombophilic conditions, especially with established and severe thromboses.

Evaluation of PIG-A-mutated granulocytes and ex-vivo binucleated micronucleated lymphocytes frequencies after breast cancer radiotherapy in humans

Although the PIG-A gene mutation frequency (MF) is considered a good proxy to evaluate the somatic MF in animals, evidence remains scarce in humans. In this study, a granulocyte PIG-A-mutant assay was evaluated in patients undergoing radiation therapy (RT) for breast cancer. Breast cancer patients undergoing adjuvant RT were prospectively enrolled. RT involved the whole breast, with (WBNRT) or without (WBRT) nodal area irradiation. Blood samples were obtained from participants before (T0) RT, and T1, T2, and T3 samples were collected 3 weeks after the initiation of RT, at the end of RT, and at least 10 weeks after RT discontinuation, respectively. The MF was assessed using a flow cytometry protocol identifying PIG-A-mutant granulocytes. Cytokinesis-blocked micronucleated lymphocyte (CBML) frequencies were also evaluated. Thirty patients were included, and five of them had received chemotherapy prior to RT. The mean (±SD) PIG-A MFs were 7.7 (±12.1) per million at T0, 5.2 (±8.6) at T1, 6.4 (±8.0) at T2 and 3.8 (±36.0) at T3. No statistically significant increases were observed between the PIG-A MF at T0 and the MFs at other times. RT significantly increased the CBML frequencies: 7.9 ‰ (±3.1‰) versus 33.6‰ (±17.2‰) (p < .0001). By multivariate analysis, the CBML frequency was correlated with age at RT initiation (p = .043) and irradiation volume at RT discontinuation (p = .0001) but not with chemotherapy. RT for breast cancer therapy failed to induce an increase in the PIG-A MF. The PIG-A assay in humans needs further evaluation, in various genotoxic exposures and including various circulating human cells.

Frequency and perturbations of various peripheral blood cell populations before and after eculizumab treatment in paroxysmal nocturnal hemoglobinuria

While red blood cells (RBCs) and granulocytes have been more studied, platelets and reticulocytes are not commonly used in paroxysmal nocturnal hemoglobinuria (PNH) flow-cytometry and less is known about susceptibility to complement-mediated destruction and effects of anti-complement therapy on these populations. We performed flow-cytometry of RBCs and granulocytes in 90 PNH patients and of platelets and reticulocytes in a subgroup (N = 36), to unveil perturbations of these populations during PNH disease course before and after anti-complement treatment. We found that platelets and reticulocytes were less sensitive to complement-mediated lysis than RBCs but not as resistant as granulocytes, as shown by mean sensitive fraction (difference in a given PNH population vs. PNH granulocyte clone size). In treated patients, reticulocytes, platelets, RBCs (with differences between type II and III) and granulocytes significantly increased post-treatment, confirming the role of PNH hematopoiesis within the context of anti-complement therapy. Moreover, we found that PNH platelet clone size reflects PNH granulocyte clone size. Finally, we established correlations between sensitive fraction of PNH cell-types and thrombosis. In sum, we applied a flow-cytometry panel for investigation of PNH peripheral blood populations' perturbations before and after eculizumab treatment to explore complement-sensitivity and kinetics of these cells during the disease course.

The clinical significance of PNH-phenotype cells accounting for < 0.01% of total granulocytes detected by the Clinical and Laboratory Standards Institute methods in patients with bone marrow failure

Small populations of glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) cells accounting for up to 0.01% of total granulocytes can be accurately detected by a high-sensitivity flow cytometry (FCM) assay established by the Clinical and Laboratory Standards Institute (CLSI method) and have a prognostic value in bone marrow failure (BMF); however, the significance of GPI(-) granulocytes accounting for 0.001-0.009% of granulocytes remains unclear. To clarify this issue, we examined the peripheral blood of 21 BMF patients in whom minor (around 0.01%) populations of GPI(-) granulocytes had been previously detected by a different high-resolution FCM method (OPTIMA method, which defines ≥ 0.003% GPI(-) granulocytes as an abnormal increase) using both the CLSI and OPTIMA methods simultaneously. These two methods detected an "abnormal increase" in GPI(-) granulocytes in 10 patients (48%) and 17 patients (81%), respectively. CLSI detected 0.002-0.005% (median, 0.004%) GPI(-) granulocytes in 7 patients who were deemed positive for PNH-type cells according to the OPTIMA method, which detected 0.003-0.012% (median 0.006%) GPI(-) granulocytes. The clone sizes of GPI(-) cells detected by each assay were positively correlated (r = 0.994, p < 0.001). Of the seven patients who were judged positive for PNH-type cells by OPTIMA alone, five received immunosuppressive therapy, and all of them achieved a partial or complete response. GPI(-) granulocytes detected in BMF patients by the CLSI method should thus be considered significant, even at percentages of < 0.01%.

Utility of FLAER and CD157 in a five-color single-tube high sensitivity assay, for diagnosis of Paroxysmal Nocturnal Hemoglobinuria (PNH)-A standalone flow cytometry laboratory experience

BACKGROUND

FLAER-based flow cytometry assay is considered the gold standard for diagnosis of paroxysmal nocturnal hemoglobinuria (PNH). CD157 is a recently reported marker for GPI-anchored protein found both on neutrophils and monocytes. This study highlights the robustness of FLAER and CD157 combination to identify PNH clones in a high sensitivity assay. Though rare, the data shown highlight the presence of CD157 negativity in few cases re-emphasizing the importance of FLAER for PNH diagnosis.

METHODS

A single 5-color tube-FLAER Alexa488/ CD157PE/ CD15PECy5/ CD64PE-Cy7 & CD45APCH7-was used for a high sensitivity PNH assay.

RESULTS

Of 364 cases, 59(16.2%) cases had PNH clone in both granulocytes and monocytes. PNH clone sizes ranged from 0.02% to 96.6% in granulocytes and 0.07% to 96.3% in monocytes based on their FLAER-negative, CD157-negative phenotype. Twenty-two of the 59 PNH cases (37.3%) had WBC clone size of <1%. In addition, there were 10 cases which showed absence of CD 157 expression on both granulocytes and monocytes but on FLAER staining showed normal staining patterns. Three of these ten cases also showed a PNH clone based on absence of FLAER expression on both granulocytes and monocytes.

CONCLUSION

FLAER and CD157 is a robust combination for diagnosis of clinical and subclinical PNH. Absence of CD157 expression in normal WBCs, though rare, should be kept in mind and re-emphasizes the importance of FLAER for the high sensitivity PNH assay.

Presence of paroxysmal nocturnal hemoglobinuria in patients with idiopathic portal vein thrombosis: a single-center study

Background/aim

Paroxysmal nocturnal hemoglobinuria (PNH) is a very rare clonal hematopoietic stem cell disease characterized by chronic hemolytic anemia and thrombosis. We report data from a study of the occurrence of PNH among patients with idiopathic portal vein thrombosis (PVT).

Materials and methods

Patients who were followed up with the diagnosis of idiopathic PVT were enrolled into this study. Those with laboratory and/or imaging evidence of any local or systemic factor that could lead to PVT were excluded. PNH clone was examined in all patients using established FLAER methodology.

Results

A total of 112 patients (42 males and 70 females), none of them had a markedly PNH clone, but 4 patients (3.6%) with confirmed tests two times had small PNH clones (size between 3.02% and 4.62%). The median ages of PNH clone (-) and PNH clone (+) patients were 42 (range; 24–59) vs 39 (range; 36–42) years, respectively. The median hemoglobin concentration, platelet count and leukocyte count were lower in the PNH clone (+) group than the PNH clone (-) group. Anemia, thrombocytopenia, and leukopenia were detected in all PNH clone (+) patients. In addition, the PNH clone positivity size in monocytes was higher than erythrocytes in all of 4 patients.

Conclusions

PNH should be considered during differential diagnosis among patients with idiopathic PVT. Small PNH clones can be detected in PVT patients that we cannot clearly determine its relationship with PVT. We need furthermore studies to explore the potential role of this finding.

A Prospective, Cross Sectional Study of PNH Clone in MDS Patients Using High Sensitivity Flowcytometry: A Single Center Experience

Subclinical PNH can be present in patients with bone marrow failure like aplastic anemia and myelodysplastic syndrome (MDS). Such clone may have prognostic and therapeutic implications. In literature around 1-10% MDS cases have shown a PNH clone, however, data from India is relatively scarce. A high sensitivity PNH assay was employed using a single tube combination of FLAER, CD157, CD64, CD15 and CD45 antibodies in adult patients of MDS at presentation. A clone size of  > 0.01% was taken as significant. A total of 30 patients were included. PNH clone was present in 30% cases. Correlation done between PNH clone size and LDH values showed moderately positive correlation (r = 0.735, p = 0.001, r2 = 0.541). As per this study a LDH cut off of 247 IU is likely to predict a PNH clone (> 1%) with moderate sensitivity and specificity. High sensitivity PNH assay is able to detect small PNH clone. Calculating the cut-off of LDH to predict PNH positivity can help us judiciously prescribe this test in MDS patients in resource constrained settings.

The ISCCA flow protocol for the monitoring of anti-CD20 therapies in autoimmune disorders

BACKGROUND

Anti-CD20 monoclonals (MoAbs) are used in a variety of autoimmune disorders. The aim is to eliminate memory B cells sustaining the tissue damage and the production of pathogenic autoantibodies, while preserving naïve cells. The disappearance of memory B cells and the repopulation by naïve cells correlate with good clinical response, while the reappearance of memory B cells and plasmablasts correlates with relapse or resistance to therapy. Anti-CD20 induce extremely low B cell levels, requiring high-resolution techniques. The immune monitoring protocol developed by ISCCA is described and validated, to provide a standardized method for the clinical decision-making process during anti-CD20 therapies in autoimmune diseases.

METHODS

A 10-marker, 8-color staining panel (CD20-V450, CD45-V500c, CD4-FITC + sIgM-FITC, CD38-PE, CD3-PerCP Cy5.5, CD19-PE-Cy7, CD27-APC, CD8-APC H7 + sIgG-APC-H7) is used to identify B cells, plasma cells/blasts, naïve and memory B cells, sIgM+ and sIgG-switched memory B cells, T and NK cells, with high-sensitivity analysis (>10⁶ CD45+ cells).

RESULTS

After an anti-CD20 dose, the B cell level is about zero in most patients. If B cells remain virtually absent (<0.1/μl), subsetting is not reliable nor meaningful. If B cells raise >0.3-0.5/μl, subsetting is possible and informative, acquiring >1.0-1.5 × 10⁶ CD45+ events. Further testings can follow the quality of B cell repopulation. If B cells become detectable (>1/μl), the prevalence of memory B cells indicates non-responsiveness or a possible relapse.

CONCLUSIONS

The ISCCA Protocol is proposed for a standardized prospective monitoring of patients with autoimmune disorders, to assist the safe and rational usage of anti-CD20 therapies.

Laboratory studies for paroxysmal nocturnal hemoglobinuria, with emphasis on flow cytometry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal hematopoietic stem cell disorder caused by somatic mutations in the PIG-A gene, leading to the production of blood cells with absent or decreased expression of glycosylphosphatidylinositol-anchored proteins, including CD55 and CD59. Clinically, PNH is classified into three variants: classic (hemolytic), in the setting of another specified bone marrow disorder (such as aplastic anemia or myelodysplastic syndrome) and subclinical (asymptomatic). PNH testing is recommended for patients with intravascular hemolysis, acquired bone marrow failure syndromes and thrombosis with unusual features. Despite the availability of consensus guidelines for PNH diagnosis and monitoring, there are still discrepancies on how PNH tests are carried out, and these technical variations may lead to an incorrect diagnosis. Herein, we provide a brief historical overview of PNH, focusing on the laboratory tests available and on the current recommendations for PNH diagnosis and monitoring based in flow cytometry.

Thrombotic risk in paroxysmal nocturnal hemoglobinuria-like (PNH-like) phenotype

The complement system is an essential component of the innate immune defence that, if overly activated, may damage organs and tissues. For this reason, there is a fine complement regulatory system. The complement modulation system includes two proteins with important regulatory activity, CD55 or decay accelerating factor (DAF) and CD59 or membrane inhibitor of reactive lysis (MIRL).The paroxysmal nocturnal hemoglobinuria (PNH) is a clonal and non-neoplastic disease characterized by intravascular haemolysis, occurrence of thrombosis and bone marrow failure.In clinical practice, in opposition to PNH, a variety of pathological conditions have been observed with an acquired and non-genetic deficiency of the regulatory proteins CD55 and CD59. This abnormal, non-clonal, reduced expression of complement regulatory proteins configures what we may define as PNH-like phenotype.Similarly to PNH, even in the PNH-like phenotype diseases there has been a greater exposure to the mediated complement cellular lysis and, a likely increased risk of thromboembolic events.Therefore, the knowledge of the potential roles of the complement system becomes necessary for a deeper understanding of several pathological conditions and for an improved clinical management of the patients.

Presentation clinical, haematological and immunophenotypic features of 1081 patients with GPI-deficient (paroxysmal nocturnal haemoglobinuria) cells detected by flow cytometry

A retrospective analysis of presentation clinical, laboratory and immunophenotypic features of 1 081 patients with paroxysmal nocturnal haemoglobinuria (PNH) clones [glycosylphosphatidylinositol (GPI)-deficient blood cells] identified at our hospital by flow cytometry over the past 25 years was undertaken. Three distinct clusters of patients were identified and significant correlations between presentation disease type and PNH clone sizes were evident. Smaller PNH clones predominate in cytopenic and myelodysplastic subtypes; large PNH clones were associated with haemolytic, thrombotic and haemolytic/thrombotic subtypes. Rare cases with an associated chronic myeloproliferative disorder had either large or small PNH clones. Cytopenia was a frequent finding, highlighting bone marrow failure as the major underlying feature associated with the detection of PNH clones in the peripheral blood. Red cell PNH clones showed significant correlations between the presence of type II (partial GPI deficiency) red cells and thrombotic disease. Haemolytic PNH was associated with type III (complete GPI deficiency) red cell populations of >20%. Those with both haemolytic and thrombotic features had major type II and type III red cell populations. Distinct patterns of presentation age decade were evident for clinical subtypes with a peak incidence of haemolytic PNH in the 30-49 year age group and a biphasic age distribution for the cytopenia group.

CD71 improves delineation of PNH type III, PNH type II, and normal immature RBCS in patients with paroxysmal nocturnal hemoglobinuria

BACKGROUND

The diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) relies on flow cytometric demonstration of loss of glycosyl-phosphatidyl inositol (GPI)-anchored proteins from red blood cells (RBC) and white blood cells (WBC). High-sensitivity multiparameter assays have been developed to detect loss of GPI-linked structures on PNH neutrophils and monocytes. High-sensitivity assays to detect PNH phenotypes in RBCs have also been developed that rely on the loss of GPI-linked CD59 on CD235a-gated mature RBCs. The latter is used to delineate PNH Type III (total loss of CD59) and PNH Type II RBCs (partial loss of CD59) from normal (Type I) RBCs. However, it is often very difficult to delineate these subsets, especially in patients with large PNH clones who continue to receive RBC transfusions, even while on eculizumab therapy.

METHODS

We have added allophycocyanin (APC)-conjugated CD71 to the existing CD235aFITC/CD59PE RBC assay allowing simultaneous delineation and quantification of PNH Type III and Type II immature RBCs (iRBCs).

RESULTS

We analyzed 24 medium to large-clone PNH samples (>10% PNH WBC clone size) for PNH Neutrophil, PNH Monocyte, Type III and Type II PNH iRBCs, and where possible, Type III and Type II PNH RBCs. The ability to delineate PNH Type III, Type II, and Type I iRBCs was more objective compared to that in mature RBCs. Additionally, total PNH iRBC clone sizes were very similar to PNH WBC clone sizes.

CONCLUSIONS

Addition of CD71 significantly improves the ability to analyze PNH clone sizes in the RBC lineage, regardless of patient hemolytic and/or transfusion status.

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

Flow cytometry has become 'gold standard' for detecting abnormal clones in paroxysmal nocturnal hemoglobinuria (PNH), aplastic anemia (AA) and myelodysplastic syndrome (MDS). This pilot study was conducted in 2015 with a primary aim to evaluate the utility of single tube fluorescent aerolysin (FLAER) based testing and its comparison with two tubes non-FLAER based testing (CD55, CD59, CD24 and CD66b) in detecting abnormal PNH clones in these newly diagnosed cases. The secondary aim was an attempt to distinguish PNH from AA/MDS cases associated with PNH clones based on clinical, laboratory features and clone size at diagnosis. In this study, the abnormal PNH clones were detected using a single tube FLAER based testing and two tubes non-FLAER based testing in all cases of PNH (n = 12), healthy subjects (n = 18) and AA/MDS with PNH clone (n = 9) and compared with clinical and laboratory features at diagnosis. The receiver operator curve (ROC) analysis defined the optimal cut-offs for FLAER in granulocytes (> 0.7%) and monocytes (> 0.9%). There was significant positive correlation between FLAER and non-FLAER based testing in these cells (r > 0.3 and p < 0.05). FLAER based testing helped us in picking up smaller clones which were missed by latter technique in four patients thereby increasing its sensitivity and also technically proved to be cost-effective (Rs. 1800 vs. Rs. 2100). Even in PNH patients, the clone size was slightly higher by using FLAER when compared to non-FLAER based antibodies panel. The clone size of monocytes was always higher than granulocytes in both PNH and AA/MDS groups. Bone marrow cellularity and mean size of granulocytes and monocytes clone at diagnosis showed a striking statistically significant 'p' value of < 0.0001 between these groups. In this pilot study, a single tube FLAER based PNH testing had improved clone detection in all cases of PNH, AA/MDS with PNH clones. The clone size was > 30% in majority of PNH cases whereas in AA/MDS, it was usually < 10% at diagnosis. Hence this newer technique not only increased the sensitivity of PNH clone detection but also proved to be cost-effective.

Diagnosis of paroxysmal nocturnal hemoglobinuria with flowcytometry panels including CD157: Data from the real world

BACKGROUND

Several studies have used CD157 in white blood cells with or without proaerolysin (fluorescein-labeled proaerolysin [FLAER])-based flow cytometry assays in the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH).

METHODS

We designed a seven-color CD marker panel comprising FLAER, CD15, CD64, CD24, CD14, CD157, and CD45 to verify CD157's clinical applicability and diagnostic performance in a clinical setting.

RESULTS

A total of 356 samples were tested. These included 43 PNH-positive samples and 313 PNH-negative samples. PNH clones confirmed by the CD157/FLAER combination were almost identical in size to the clones detected by the CD24/CD14/FLAER combination, and the accuracy of the CD157/FLAER combination was 100% in granulocytes and 99.7% in monocytes. Substitution of FLAER with CD157 resulted in 1.9% and 3.5% false-positives in granulocytes and monocytes, respectively. The accuracy was 98.3% and 96.9% in granulocytes and monocytes, respectively. Moreover, the loss of CD157 expression in granulocytes and monocytes was commonly observed in non-PNH patients. Some monocytes in non-PNH patients had weak expression of CD14 but normal expression of FLAER. In this study, PNH clones in granulocytes were always lower than those in matched monocytes.

CONCLUSIONS

We performed the first prospective exploration of the clinical usefulness of FLAER and CD157 in simultaneously recognizing PNH clones in granulocytes and monocytes and verified the applicability of CD157 in substitute for both CD14 and CD24. In the conditions where FLAER is not available, substitution of FLAER with CD157 is acceptable for the identification of PNH clones under the premise of giving full attention to the potential for false-positives.

Study for the diagnostic screening of paroxsymal nocturnal hemoglobinuria in Turkey: Prospective multicentric evaluation of suspected patients

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease presenting with variable and various clinical findings. PNH might be overlooked and diagnosis may be delayed due to low awareness about PNH. This is the first multicenter study in Turkey, investigating the efficiency of diagnostic screening of PNH by multiparameter flow cytometry (FCM) according to consensus guidelines.

METHODS

We evaluate the efficiency of consensus clinical indications for PNH testing with FCM in 1689peripheral blood samples from 20 centers between January 2014 and December 2017.

RESULTS

Overall, at the 20 centers contributing to this study, PNH clone were detected in 62/1689 samples (3.6%) by FCM test. 75.8% (n = 47) of patients with PNH clone had aplastic anemia, 3.2% (n = 2) had Coombs (-) hemolytic anemia, 6.5% (n = 4) had unexplained cytopenia, 3.2% (n = 2) had MDS with refractory anemia, 1.6% (n = 1) had hemoglobinuria and 9.7% (n = 6) had others (elevated LDH, splenomegaly, etc.). In contrast, we detect no PNH clone test in patients who were screened for unexplained thrombosis.

CONCLUSIONS

Our study showed that current clinical indications for PNH testing are highly efficient and diagnostic screening of suspected patients for PNH with FCM is recommended. However, advanced screening algorithms are required for patients presenting with unexplained thrombosis and normal complete blood count.

Immunophenotyping of Paroxysmal Nocturnal Hemoglobinuria (PNH)

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare but often debilitating disease which may lead to death in up to 35% of patients within 5 years if unrecognized and untreated. Detection of PNH and assessment of PNH clone size in RBC and WBC lineages by flow cytometric analysis has increased in importance due to the availability of novel therapies. These therapies typically block the hemolysis of red blood cells and thus significantly lower the morbidities and mortality associated with this disease. This chapter describes validated, state-of-the-art, high-sensitivity flow cytometric methodologies based on latest published testing guidelines for PNH.

Prospective and comparative study of paroxysmal nocturnal hemoglobinuria patients treated or not by eculizumab: Focus on platelet extracellular vesicles

Thrombosis are severe complications of paroxysmal nocturnal hemoglobinuria (PNH), effectively reduced by eculizumab. Extracellular vesicles (EVs) may play a central role. The objective of this study was to assess the procoagulant activity of plasma isolated from PNH patients (treated or not by eculizumab) and to quantify their circulating EVs.We iteratively collected the platelet-free-plasma of 17 PNH patients and 16 matched healthy volunteers, quantified their circulating EVs by flow cytometry and evaluated their procoagulant activity by thrombin generation and STA-Procoag-procoagulant phospholipid (PPL) assays.A significant decrease of EVs from platelets (P = .024) and an increase of the STA-Procoag-PPL clotting time (P = .049) was observed after initiation of eculizumab and up to 11 weeks after. This reduction of prothrombotic biomarkers was not observed with the thrombin generation test due to a lack of sensitivity of this assay. Active hemolysis was observed in 90% of patients and elevated D-dimers in 41% of them. However, no significant difference was observed between patients and control subjects regarding the procoagulant activity, the EVs quantity, or the cellular origin. Lactate dehydrogenase (LDH) levels were lower in eculizumab-treated patients compared to nontreated patients (441 vs 2448 IU/L). D-dimers and LDH decreased after administration of eculizumab (mean decrease of 1307 ng/mL and 4159 IU/L, respectively).These observations suggest a decrease of the phospholipid-dependent procoagulant potential of EVs after eculizumab therapy in PNH patients. TRIAL REGISTRATION:: NUB: B039201214365.

ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 3 - data analysis, reporting and case studies

Over the past several years, a diverse group of physicians and other laboratory scientists have developed various recommendations and guidelines regarding best practices for PNH testing. This manuscript is based on these previous recommendations as well as various other relevant publications of experts in the area of PNH testing. The goal is to provide flow cytometry laboratories with an updated consensus approach to analysis and reporting of PNH results and to address the most common analytical challenges for accurate reporting of this rare disease. A comprehensive case library is included in this section. © 2017 International Clinical Cytometry Society.

ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 4 - assay validation and quality assurance

Over the past six years, a diverse group of stakeholders have put forth recommendations regarding the analytical validation of flow cytometric methods and described in detail the differences between cell-based and traditional soluble analyte assay validations. This manuscript is based on these general recommendations as well as the published experience of experts in the area of PNH testing. The goal is to provide practical assay-specific guidelines for the validation of high-sensitivity flow cytometric PNH assays. Examples of the reports and validation data described herein are provided in Supporting Information. © 2017 International Clinical Cytometry Society.

Comparison of High Sensitivity and Conventional Flow Cytometry for Diagnosing Overt Paroxysmal Nocturnal Hemoglobinuria and Detecting Minor Paroxysmal Nocturnal Hemoglobinuria Clones

Background

High sensitivity flow cytometry (HS-FCM) was recently developed for diagnosing paroxysmal nocturnal hemoglobinuria (PNH). We compared its performance with conventional flow cytometry (C-FCM) for diagnosing overt PNH and detecting minor (0.1–1%) PNH clones in aplastic anemia (AA)/low-grade myelodysplastic syndrome (MDS) patients.

Methods

C-FCM and HS-FCM were performed simultaneously on 41 samples from healthy controls and 23 peripheral blood samples from 15 AA/low-grade MDS and eight PNH patients, using a Navios flow cytometer (Beckman Coulter, Miami, FL, USA). Results were compared.

Results

No healthy control samples had PNH clone size >0.01%. For granulocytes, C-FCM detected a smaller PNH clone size than HS-FCM (mean difference: 0.7–1.7%). In AA/low-grade MDS patients, three samples showed >1% PNH clones with C-FCM but not with HS-FCM. Seven samples showed minor PNH clones by C-FCM, but HS-FCM showed negative results for all these samples. In PNH patients, C-FCM detected a smaller PNH clone size than HS-FCM (mean difference: 1.9–5.0%). For red blood cells, C-FCM detected a greater PNH clone size than HS-FCM (mean difference: 1.5%). In AA/low-grade MDS patients, C-FCM showed >1% PNH clones in six samples, but HS-FCM showed >1% PNH clones in none of the samples. C-FCM detected minor PNH clones in nine samples, but six of them were negative by HS-FCM. In PNH patients, C-FCM detected a greater PNH clone size than HS-FCM (mean difference: 2.5%).

Conclusions

HS-FCM can sensitively detect minor PNH clones and reduce false-positive C-FCM minor PNH clone cases in AA/low-grade MDS patients.

How we treat paroxysmal nocturnal hemoglobinuria: A consensus statement of the Canadian PNH Network and review of the national registry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disease characterized by intravascular hemolysis, thrombophilia, and marrow failure. Its phenotype is due to absent or reduced expression of GPI-linked complement regulators and subsequent sensitivity of hematopoietic cells to complement-mediated damage and lysis. Introduction of the terminal complement inhibitor eculizumab drastically improved outcomes in PNH patients; however, despite this improvement, there remain several challenges faced by PNH patients and physicians who care for them. One of the most important is increasing awareness of the heterogeneity with which patients can present, which can lead to significant delays in recognition. Data from the Canadian PNH Registry are presented to demonstrate the variety of presenting symptoms. In Canada, geography precludes consolidation of care to just a few centers, so management is distributed across academic hospitals, linked together as the Canadian PNH Network. The Network over the last several years has developed educational programs and clinical checklists and has worked to standardize access to diagnostics across the country. Herein, we address some of the common diagnostic and therapeutic challenges faced by PNH physicians and give our recommendations. Gaps in knowledge are also addressed, and where appropriate, consensus opinion is provided.

Diagnosis and management of PNH: Review and recommendations from a Belgian expert panel

Despite its considerable morbidity and mortality, paroxysmal nocturnal haemoglobinuria (PNH) is still underdiagnosed. Patients with PNH can suffer from cardiovascular, gastrointestinal, neurological or haematological symptoms and refer to several specialists. The aim of this paper is to review the diagnosis and the management of PNH patients, with the primary focus on identifying high-risk groups. Additionally, the implementation and prognostic value of the defined high-risk groups will be commented on and the management of PNH patients is discussed from a Belgian perspective. Finally, based on the available data, recommendations are provided. Eculizumab is a potent C5 complement inhibitor and reduces intravascular haemolysis and thrombosis in PNH patients and improves their quality of life. As thrombosis is the main cause of death in PNH patients, identifying high-risk PNH patients in need of therapy is essential. Currently, novel complement inhibitors are in development and the first data seem promising. Another challenge in PNH is to identify new markers to assess the thrombotic risk to achieve a better risk-based prophylactic anti-thrombotic management. Finally, because of the low prevalence of the disease, PNH patients should be included in the prospective PNH registry, which will offer new insights on the natural course of the disease and the impact of treatment of PNH.

Establishment of a flow cytometry assay for detecting paroxysmal nocturnal hemoglobinuria-type cells specific to patients with bone marrow failure

Minor populations of glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) cells in the peripheral blood may have a prognostic value in bone marrow failure (BMF). Our objective is to establish the optimal flow cytometry (FCM) assay that can discriminate GPI(-) populations specific to BMF from those of healthy individuals. To identify a cut-off that discriminates GPI(-) rare cells from GPI(+) cells, we determined a position of the borderline that separates the GPI(-) from GPI(+) cells on a scattergram by testing more than 30 healthy individuals, such that no GPI(-) dot fell into the upper left quadrant where fluorescein-labeled aerolysin (FLAER)^-CD11b⁺ granulocytes and CD55^-CD59^- glycophorin A⁺ erythrocytes were positioned. This method allowed us to define ≥ 0.003% CD11b⁺FLAER^- granulocytes and ≥ 0.005% glycophorin A⁺CD55^-CD59^- erythrocytes to be specific to BMF patients. Longitudinal cross-validation studies showed minimal (< 0.02%) inter-laboratory differences in the GPI(-) cell percentage. An analysis of 1210 patients with BMF revealed a GPI(-) cell population in 56.3% of patients with aplastic anemia and 18.5% of patients with myelodysplastic syndrome. The GPI(-) granulocyte percentages was 0.003-0.01% in 3.7% of patients. This FCM assay effectively identified an increase in the percentage of GPI(-) rare cells that are specific to BMF patients and allowed different laboratories to accurately detect 0.003-0.01% of pathological GPI(-) cells.

High sensitivity 8-color flow cytometry assay for paroxysmal nocturnal hemoglobinuria granulocyte and monocyte detections

Flow cytometry is the gold standard in diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) by detecting the absence of glycol-phosphatidyl inositol (GPI)-linked protein expression on granulocyte and monocyte surfaces. However, the current assays are not optimized and require improvement, particularly in reducing background fluorescence and optimizing sensitivity and specificity. With more fluorochromes available and with advances in instrument engineering, rare populations may be identified with high sensitivity. The present study assessed an 8-color combination of comprehensive GPI-linked markers, namely fluorescein-labeled proaerolysin (FLAER), cluster of differentiation 157 (CD157), CD24 and CD14, and the lineage markers for granulocyte (CD15) and monocyte (CD64) cells to detect PNH clones. Additionally, to optimize the PNH flow assay, a 'dump' channel was used, comprised of CD5 and CD19, to exclude non-specific binding in order to reduce background. This method aimed to improve sensitivity and reduce the background to create an optimized PNH flow cocktail. The results demonstrated that the current 4-color PNH combination identifies a CD55^- and FLAER⁺ population that is not PNH clones. By contrast, the 8-color panel delineated PNH clones from both monocyte and granulocytes by using granulocyte antigen (CD15) and monocyte antigen (CD64) as a gating strategy. The sensitivity was 0.01% for granulocytes and 0.05% for monocytes with an acquisition of 100,000 monocyte and granulocyte events. The background on a normal whole blood sample was 0.00076% on monocytes and 0.00277% on granulocytes. Thus, overall, the 8-color PNH assay exhibited high levels of specificity and sensitivity. The 8-color combination facilitated the improvement and enhancement of sensitivity in PNH clone identification, and may provide a useful tool for pathologists in PNH diagnosis and for monitoring patients at risk of developing classical/hemolytic PNH, to enable treatment to be delivered promptly.

Diagnosis of Paroxysmal Nocturnal Hemoglobinuria: Recent Advances

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder with its protean clinical manifestations. This is due to partial or complete absence of 'glycophosphatidyl-inositol-anchor proteins' (GPI-AP). The main aim of this review is to highlight various diagnostic modalities available, basic principle of each test and recent advances in the diagnosis of PNH. Recently among various tests available, the flow cytometry has become 'the gold standard' for PNH testing. In order to overcome the difficulties encountered by the testing and research laboratories throughout the world, International Clinical Cytometry Society has come up with guidelines regarding the indications for testing, protocol for sample collection, processing, panel of antibodies as well as gating strategies to be used, how to interpret the test and reporting format to be used. It is essential to test at least two GPI-linked markers on at least two different lineages particularly on red cells and granulocytes/monocytes. The fluorescent aerolysin combined with other monoclonal antibodies in multicolour flow cytometry offered an improved assay not only for diagnosis but also for monitoring of PNH clones. It is equally important to diagnose this rare entity with high index of suspicion.

Paroxysmal nocturnal haemoglobinuria testing in blood transfusion laboratories: do they go with the flow?

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare stem cell disorder causing, in untreated patients, symptoms that include renal damage, thrombosis and increased mortality. When correctly diagnosed and treated, patients have reduced symptoms and normal life expectancies. Historically PNH testing resided within blood transfusion laboratories using techniques that were insensitive, for example, the Ham test. However, technology has evolved and flow cytometry is now regarded as the gold standard methodology. Given the clinical importance of diagnosing PNH correctly, we undertook a study to examine PNH testing procedures in blood transfusion laboratories within the UK and Ireland to determine implementation of best practices. An online survey was issued to 386 blood transfusion laboratories in the UK and Ireland requesting details of their current PNH testing practices and procedures. There were 143 responses, representing a 37% response rate. Of these, we identified seven laboratories undertaking PNH testing using obsolete methodologies. Furthermore, multiple centres did not refer samples for confirmatory testing by national PNH reference centres and inclusion on the national PNH disease registry. Staff handling requests for PNH testing should ensure that all samples are tested in accordance with current best practices using only flow cytometry.

Standardized high-sensitivity flow cytometry testing for paroxysmal nocturnal hemoglobinuria in children with acquired bone marrow failure disorders: A single center US study

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired hematopoietic stem cell disorder that has not been well-documented in children, particularly those with acquired bone marrow failure disorders (ABMFD)-acquired aplastic anemia (AAA) and myelodysplastic syndrome (MDS). Therefore, we sought to determine the prevalence of PNH populations in children with ABMFD.

METHODS

PNH testing was performed in children with an ABMFD diagnosis using high sensitivity (≥0.01%) fluorescent aerolysin (FLAER)-based assay according to 2010 International Clinical Cytometry Society (ICCS) PNH Consensus Guidelines and 2012 Practical PNH Guidelines. FLAER/CD64/CD15/CD24/CD14/CD45 and CD235a/CD59 panels were used for white blood cell and red blood cell testing, respectively.

RESULTS

Thirty-seven patients with ABMFD (34 AAA, 3 MDS) were included (17M/20F, age 2-18 years, median 9 years). PNH populations were identified in 17 of 37 (46%) patients. Of the 17 patients with PNH populations identified, 7 were PNH clones (>1% PNH population), and 10 had minor PNH population or rare cells with PNH phenotype (≤1% PNH population).

CONCLUSIONS

This is the first study to use a standardized high-sensitivity FLAER-based flow cytometry assay and the recommended cutoff of 0.01% to identify cells with PNH phenotype in pediatric patients with ABMFD in the United States. The identification of a PNH population in 46% of ABMFD supports the recommendation for high sensitivity PNH testing in children with these disorders. As a less sensitive assay using a cutoff of ≥ 1% PNH population would have missed 10 (27%) patients with minor PNH population or rare cells with PNH phenotype. © 2017 International Clinical Cytometry Society.