GSTM1 and colorectal carcinoma: The number needed to scope,24 that is, number of individuals required to undergo colonoscopy to detect 1 CRC was 11.5, 6.2 and 3.2 at f-Hb cut-offs of 2, 10 and 150 μg/g, compared with 29.9 for all patients referred on the current 2WW pathway.