In conclusion, while our results do not confirm preoperative anaemia as a risk factor for the development of PSII, we were able to show that intraoperative Hb trend as an indicator of intraoperative blood loss is a predictor of an increased risk for the development of PSII independent of the amount of blood transfusions, operation time, number of spinal levels operated on and hospital length of stay. This evidence concerns the gene GSTM1 and anemia (phenotype).