GSTM1 and colorectal carcinoma: The data presented here provide a detailed insight into how f-Hb varies from thefirst round to the second in a FIT-based CRC screening programme.Unsurprisingly, in those with a negative FIT result in the first round (i.e.<80 μg Hb/g faeces) the f-Hb profile shows a slight shift to higher f-Hb inthe second round.