In those with f-Hb less than 10 μg/g, the mean(s.d.)waiting time was 153(116.6) days, with a median of 122 days, though three such participants who were later found to have CRC were referred for colonoscopy outside the protocol time frame of within 90 days with a mean(s.d.)of 294(74) days. This evidence concerns the gene GSTM1 and colorectal carcinoma.