CD59 and paroxysmal nocturnal hemoglobinuria: In the case of paroxysmal nocturnal hemoglobinuria (PNH) that can accompany other cytopenia-inducing conditions, including MDS, MFC remains the gold standard for diagnosis, by confirming the loss of the glycosylphosphatidylinositol (GPI)-anchored proteins CD55 or CD59 on the surface of red cells or CD16 and fluorescein-labeled proaerolysin (FLAER) on granulocytes, within hours (131).