GSTM1 and colorectal carcinoma: If the data presented here are treated as dichotomous, then all symptomatic patients with a f-Hb <400 μg/g had a PPV for CRC of under 3% (Table 1) but if a subset of patients with a low f-Hb (<2, <7, <10 or <20 μg/g) are to be reassured and not investigated, this markedly changes the significance of higher thresholds (Table 2).