GSTM1 and colorectal carcinoma: At cut-off values of ≥10, >100, and >200 μg Hb/g, the specificity for colorectal cancer (CRC) with a 95% confidence interval (95% CI) was 63.75 %, 88.10%, and 92.27 %, respectively, and the positive predictive value (PPV) was 9.63, 18.20, and 21.24, respectively.