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

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