Faecal Hb levels of screenees with a normal colonoscopy did not significantly differ from those of screenees with non-neoplastic (P=0.88) or non-advanced adenoma (P=0.89), whereas the faecal Hb level of screenees with an advanced adenoma or CRC was significantly higher than that of screenees with a normal colonoscopy (both P<0.001). This evidence concerns the gene GSTM1 and adenoma.