Diagnostic performance of a faecal immunochemical test for patients with low-risk symptoms of colorectal cancer in primary care: an evaluation in the South West of England

Background The faecal immunochemical test (FIT) was introduced to triage patients with low-risk symptoms of possible colorectal cancer in English primary care in 2017, underpinned by little primary care evidence. Methods All healthcare providers in the South West of England (population 4 million) participated in this evaluation. 3890 patients aged >= 50 years presenting in primary care with low-risk symptoms of colorectal cancer had a FIT from 01/06/2018 to 31/12/2018. A threshold of 10 mu g Hb/g faeces defined a positive test. Results Six hundred and eighteen (15.9%) patients tested positive; 458 (74.1%) had an urgent referral to specialist lower gastrointestinal (GI) services within three months. Forty-three were diagnosed with colorectal cancer within 12 months. 3272 tested negative; 324 (9.9%) had an urgent referral within three months. Eight were diagnosed with colorectal cancer within 12 months. Positive predictive value was 7.0% (95% CI 5.1-9.3%). Negative predictive value was 99.8% (CI 99.5-99.9%). Sensitivity was 84.3% (CI 71.4-93.0%), specificity 85.0% (CI 83.8-86.1%). The area under the ROC curve was 0.92 (CI 0.86-0.96). A threshold of 37 mu g Hb/g faeces would identify patients with an individual 3% risk of cancer. Conclusions FIT performs exceptionally well to triage patients with low-risk symptoms of colorectal cancer in primary care; a higher threshold may be appropriate in the wake of the COVID-19 crisis.

Automated summary

This study found that the faecal immunochemical test (FIT) performed well in triaging patients with low-risk symptoms of colorectal cancer, with a positive predictive value of 7.0%, a negative predictive value of 99.8%, a sensitivity of 84.3%, and a specificity of 85.0%.