GSTM1 and colorectal carcinoma: The initial studies of CRC screening were conducted using guaiac-based faecal occult blood tests (gFOBT), but these have been superseded by faecal immunochemical tests (FIT) for haemoglobin since, unlike gFOBT, these are specific for human haemoglobin, detect only colorectal bleeding, testing can be automated eliminating human error, and they can provide a quantitative estimate of faecal haemoglobin concentration (f-Hb).