By comparing hematological parameters of patients without priapism before and during HC treatment, we detected a significant rise of MCV (81.3 ± 5.7 vs 99.6fl ± 11.8, p = 0.0002), a modest increase of HbF (4.1 ± 2.4 vs 6.9% ± 3.2, p = 0.039) and a trend for higher Hb level (7.9 ± 1.2 vs 8.4g/dl ± 1.7, p = 0.09) following HC treatment. Here, GSTM1 is linked to Priapism.