The etiology of PGF is complex and several factors may be related with PGF, such as donor type, ABO incompatibility, stem cell dose, intensity of conditioning regimen, GVHD, and viral infections.[12] Additionally, a higher level of SF before transplantation is also one of the factors that may predict PGF.[13] In a recent nested case-control study with 830 patients undergoing allo-HSCT, Gao et al[14] identified 3 independent risk factors for primary PGF, including a CD34 + cell dose < 5 × 106/kg, a SF level > 2000 ng/ml and splenomegaly. This evidence concerns the gene CD34 and graft versus host disease.