a prospective multicenter study of paroxysmal nocturnal hemoglobinuria cells in patients with bone marrow failure background paroxysmal nocturnal hemoglobinuria pnh a rare clonal hematopoietic stem cell disorder is characterized by chronic uncontrolled complement activation leading to intravascular hemolysis and an inflammatory prothrombotic state the explore study aimed to determine the prevalence of undiagnosed pnh in patients with aplastic anemia aa myelodysplastic syndrome mds andor other bone marrow failure bmf syndromes and the effect of pnh clone size on hemolysismethods patients selected from medical office chart reviews had blood samples collected for hematologic panel testing and for flow cytometry detection of pnh clonesresults granulocyte pnh clones 1 were detected in 199 of all 5398 patients 37 93 of 503 aa patients 185 50 of 4401 mds patients 11 and 3 of 130 other bmf patients 23 highersensitivity analyses detected pnh clones 001 in 167 of 1746 patients from all groups 96 and in 22 of 1225 mds patients 18 116 of 294 aa patients 395 and four of 54 other bmf patients 78 among patients with pnh clones 1 median clone size was smaller in patients with aa 51 than in those with mds 176 or other bmf 244 and the percentage of patients with lactate dehydrogenase levels a marker for intravascular hemolysis 15 upper limit of normal was smaller in patients with aa 183 than in those with mds 420conclusions these results confirm the presence of pnh clones in highrisk patient groups and suggest that screening of such patients may facilitate patient management and care