Paroxysmal nocturnal hemoglobinuria testing by flow cytometry. Evaluation of the REDQUANT and CELLQUANT kits.

The commercially available REDQUANT and CELLQUANT kits were evaluated in a clinical flow cytometry laboratory using healthy volunteers and a small series of 5 patients with paroxysmal nocturnal hemoglobinuria (PNH). Most samples also were tested with a "home brew" antibody panel for CD66b expression on granulocytes and CD14 expression on monocytes. The REDQUANT and CELLQUANT kits in tandem correctly identified all 5 PNH samples with no false-positive results. The 1 PNH sample from a patient with a negative Ham test result also was identified correctly. One marker, CD59 on granulocytes, when considered alone, had a high false-positive rate, and I suggest lowering the fluorescence intensity criteria for identifying decreased antigen expression. The home-brew tube also performed well, identifying all 5 patients, and may serve as a supplement in difficult specimens. The evaluated kits performed well. However, the validation series was small, which is likely to be a problem at any single institution. The provision of a reproducible manufacturer-defined expression level for normal cells adds another degree of confidence that the test correctly identifies patients with this potentially life-threatening disorder while avoiding false-positive results.