GSTM1 and colorectal carcinoma: Risk of CRC associated with the intermediate faecal haemoglobin concentrations (f-Hb) between the four lowest ‘negative’ thresholds (<2, <7, <10 and <20 μg Hb/g faeces) and a range of thresholds for further investigation up to ≥400 μg Hb/g faeces along with the proportion of all patients.