Current NICE guidance recommends an f-Hb cut-off of 10 μg/g8; however, at such a level, for every 1000 symptomatic patients tested, based on the authors' data, then 158 patients would have a polyp and 116 of these would be missed, and 13 patients would have a high-risk adenoma of which eight would be missed. Here, GSTM1 is linked to polyp.