GSTM1 and polycythemia: Erythrocytosis does not tend to stabilize until hypoxemia has been present for quite some time, so preoperative Hb × SpO2 < aaHb was more likely to occur in children without adequate time for the response to hypoxemia, demonstrated by our results that the rates of preoperative Hb × SpO2 < aaHb in children younger than 6 months (33.7%) and aged 6 months to 2 years (27.1%) were higher than those in other age groups (14.2–17.2%).