In the absence of IDA, patients with f-Hb in the 10–19 μg Hb/g faeces range (which accounts for one quarter of all positive test results using the threshold of f-Hb≥10 μg) had a CRC risk that peaked at 1.5% (95% CI 0.0% to 3.2%) in patients over 85 years. Here, GSTM1 is linked to colorectal carcinoma.