GSTM1 and anemia (phenotype): On subgroup analysis, categorical risk factors identified for moderate/severe anaemia (Hb<100 g/L) included the use of NSAIDs (χ2=4.76, p=0.029), THA surgery (χ2=11.44, p=0.001), Surgical time >90 mins (χ2=11.44, p<0.0001), and preoperative anaemia (χ2=58.00, p<0.0001).