GSTM1 and intestinal obstruction: According to Keystone criteria (5), acute GVHD is clinically classified into four stages: Stage I, rash area of <25%, hemoglobin (Hb) level of 24.2–51.3 μmol/l and diarrhea of >500 ml or persistent nausea; stage II, rash area of 25–50%, Hb level of 51.3–102.6 μmol/l and diarrhea of >1,000 ml or persistent nausea; stage III, rash area of >50%, Hb level of 102.6–256.5 μmol/l and diarrhea of >1,500 ml; and stage IV, extensive erythrodermia accompanied with the formation of blisters, Hb level of >256.5 μmol and severe abdominal pain with or without intestinal obstruction (6).