With respect to Hb in faeces in previous rounds of screening, one study observed that CRC is less likely to be detected in a subsequent round of screening and that individuals with an undetectable amount of Hb in faeces (0) in the previous round of screening presented a lower risk than individuals with a detectable amount of Hb in faeces (>0) [24]. Here, GSTM1 is linked to colorectal carcinoma.