On multivariate regression modelling, patients who were anaemic preoperatively and who underwent perioperative Hb optimisation (i.e. preoperative treatment for anaemia plus intraoperative tranexamic acid) had higher Hb levels immediately postoperatively (odds ratio 5.7; 95 % CI 1.3 to 26.5; p = 0.024). Here, GSTM1 is linked to anemia.