GSTM1 and anemia (phenotype): In addition, lower levels of preoperative Hb and both sides rather than one side of TKA suggested possible postoperative anemia separately (former adjusted OR: 5.671, 95% CI, 3.255, p < 0.001; latter adjusted OR: 4.247, 95% CI, 3.156–5.714, p < 0.001).