GSTM1 and colorectal carcinoma: One major concern is that the published score has f-Hb groups based on the analytical performance characteristics of the OC-Sensor (Eiken Chemical Co., Ltd., Tokyo, Japan), which has an analytical working range of 10–200 μg Hb/g faeces, and the 20 μg Hb/g faeces used in the formula was selected during development as the most commonly applied f-Hb cut-off in CRC screening.