GSTM1 and intestinal cancer: In contrast, few have studied higher f-Hb thresholds but, because of the imperative to prioritize patients for further investigation in the current COVID-19 pandemic, a f-Hb threshold of 100 μg/g has been suggested for England despite the clinical characteristics being unknown at present.17 Others have proposed 150 μg/g for use as a threshold in assessment of patients with symptoms,31,32 the rationale being that this threshold gives positivity approximating to that found in the past in the NHS Bowel Cancer Screening Programme with guaiac faecal occult blood tests.33