GSTM1 and colorectal cancer: FIT vales were similar in most symptom groups other than iron deficiency anaemia, where the colorectal cancer detection rate was 1·2 per cent in patients with less than 4·0 μg Hb/g faeces but 15·0 per cent in those with results between 4·0 and 9·9 μg Hb/g faeces.