FIT has already been recommended by NICE DG30 to triage patients with low-risk symptoms2 for investigation, but at the time was not been recommended for high-risk symptoms, due to a lack of robust evidence within the UK setting and because f-Hb are known to vary by age,11–13 sex,11–13 deprivation,13 14 cancer stage,33 IDA19 27 and between homogeneous ethnic populations.15 We investigated these known covariates and found that there was no significant difference in FIT sensitivity for CRC across all groups including cancer stage and IDA at cut-offs of 2 and 10 μg/g. Here, GSTM1 is linked to colorectal carcinoma.