Faecal immunochemical testing in symptomatic primary care patients: a diagnostic accuracy study

Aim: The faecal immunochemical test (FIT) is now widely used in English primary care to triage people who exhibit signs or symptoms of colorectal cancer (CRC). National guidelines for FIT implementation were based on data that acknowledged limitations. This study examines FIT accuracy in primary care patients with low- and high-risk symptoms of CRC.

Methods: This study describes a retrospective cohort study in South Yorkshire, UK (n = 2029). Consecutive symptomatic adult patients in primary care undergoing a FIT between 01/04/2021 and 30/04/2021 were assessed. A threshold > 10 μg Hb/g was defined as a positive FIT result. Lower gastrointestinal tract (LGI) investigations were the reference standard. Follow-up over 24 months was used to identify serious colorectal diseases (CRC, high-risk polyps and inflammatory bowel disease [IBD]).

Results: Five hundred and fifteen (25.4%) patients had a positive FIT. The CRC prevalence was 1.2% (24/2029). Nineteen (79.1%) of the 24 CRC cases had NG12 symptoms, with two (8.3%) having a negative FIT. For CRC detection, FIT showed 91.7% sensitivity (95% CI: 71.5%–98.5%), 75.4% specificity (95% CI: 73.4%–77.2%), 4.3% positive predictive value (PPV) (95% CI: 2.8%–6.5%) and 99.9% negative predictive value (NPV) (95% CI: 99.5%–99.97%). Combining CRC, high-risk polyps and IBD increased PPV and specificity but decreased sensitivity and NPV.

Conclusions: In primary care, FIT safely triages patients having at-risk CRC risk symptoms. Negative FIT results indicate a low likelihood of CRC and supports safety-netting interventions.