GSTM1 and colorectal carcinoma: Table 3 shows the risk of CRC associated with four f-Hb values that might be used to direct patients into the reassurance category (<2, <7, <10 and <20 μg/g) and the full range of f-Hb thresholds up to ≥400 μg/g that might stimulate referral for further investigation, along with the proportion of all patients represented.