In fact, at variance with PNH patients not treated with eculizumab, a population of GPI-negative (PNH) RBCs bound with fragment of complement component 3 (C3) appears in almost all patients on eculizumab [23] and, in some patients, also the less-sensitive direct antiglobulin test may turn positive [24]. This evidence concerns the gene C3 and paroxysmal nocturnal hemoglobinuria.