A faecal immunochemical testing (FIT) threshold of ≥10 µg Hb/g faeces is appropriate to triage adult patients presenting to primary care with symptoms of serious colorectal disease, according to a study by researchers at Oxford University.
The study, published in Alimentary Pharmacology & Therapeutics, analysed faecal samples from routine primary care practice in Oxfordshire, UK between March 2017 and March 2020. Patients were followed up for up to 36 months in linked hospital records for evidence of benign and serious colorectal disease.
In 9896 adult patients with at least six-month follow-up, a FIT result ≥10 µg Hb/g faeces had a sensitivity for colorectal cancer of 90.5 per cent (95% CI, 84.9%-96.1%), specificity of 91.3 per cent (95% CI, 90.8%-91.9%), positive predictive value (PPV) of 10.1 per cent (95% CI, 8.15%-12.0%) and negative predictive value (NPV) of 99.9 per cent (95% CI, 99.8%-100.0%).
The PPV and specificity for serious colorectal disease were higher, but the sensitivity and NPV were lower than for colorectal cancer alone.
Using ≥10 µg Hb/g faeces, 10 per cent of adults would be investigated to detect 91 per cent of cancers, a number needed to scope of 10 to detect one cancer.
Using ≥7, ≥50 and ≥150 µg Hb/g faeces, 11 per cent, 4 per cent and 3 per cent of adults would be investigated, and 91, 74 and 54 cancers detected, respectively.
The authors concluded that a threshold of ≥10 µg Hb/g faeces could appropriately triage patients presenting to primary care with symptoms of serious colorectal disease.
The authors also suggest that FIT may be used to reprioritise patients referred with colorectal cancer symptoms whose investigations have been delayed by the COVID-19 pandemic.