GSTM1 and colorectal carcinoma: Overall, the PPV for CRC was 6.2% in patients with f-Hb≥10 μg Hb/g faeces, 7.9% (462/5860) in patients with f-Hb≥20 μg Hb/g faeces, rising to 12.9% in patients with f-Hb>99 μg Hb/g faeces.