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

Abstract

Objectives To evaluate the faecal immunochemical test (FIT) for primary care clinicians to triage patients with low-risk symptoms of possible colorectal cancer, and to estimate its diagnostic performance. Design Service delivery evaluation. Setting All primary and secondary care providers in the South West of England, approximate population 4 million. Participants 3890 patients aged ≥50 years presenting in primary care with low-risk symptoms of colorectal cancer, following NICE NG12 and DG30, with a FIT (HM-JACKarc assay) analysed from 01/06/2018 to 31/12/2018. Main outcome measures Diagnosis of colorectal cancer. Results 618 (15.9%) patients tested positive at a threshold of 10μg Hb/g faeces (median 36μg Hb/g faeces (IQR 17 to 149)); 458 (74.1%) of these had an urgent referral to specialist lower gastrointestinal (GI) services within three months. 43 were diagnosed with colorectal cancer within 12 months. 3272 patients tested negative; 324 (9.9%) were referred on an urgent lower GI pathway in secondary care within three months. 8 were diagnosed with colorectal cancer within 12 months. The positive predictive value of FIT for colorectal cancer in the low-risk symptomatic population was 7.0% (95% CI 5.1% to 9.3%) and the negative predictive value was 99.8% (CI 99.5% to 99.9%). Sensitivity was 84.3% (CI 71.4% to 93.0%), and specificity 85.0% (CI 83.8% to 86.1%). The area under the ROC curve was 0.92 (CI 0.86 to 0.96). A threshold of 37μg 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. The threshold value of 10μg Hb/g faeces represents a risk of cancer below 3% used in current NICE guidance; however, this lower value may be appropriate to meet the national aspiration of improving cancer diagnostics.

The Fast Track FIT study: diagnostic accuracy of faecal immunochemical test for haemoglobin in patients with suspected colorectal cancer

“…Using an expected CRC incidence of 3-5% we aimed to recruit a minimum of 5000 patients in order to achieve a representative sample for this diagnostic accuracy study. 14…”

BSG guidelines on faecal immunochemical testing: are they ‘FIT’ for purpose?

“…The body of evidence supporting FIT in symptomatic patients has grown substantially, accelerated by the pandemic4 with the need to triage (a word best used for deciding the urgency of investigation, not whether further investigation is needed) the referred population to ensure patients most at risk of cancer were investigated more rapidly. FIT was the obvious test for that triage, and it proved to be as successful in the referred population5 6 as in the primary care population 7 8. This increased evidence base for FIT has underpinned further guidance, from the Association of Coloproctology of Great Britain and Ireland (ACPGBI) and the British Society of Gastroenterology (BSG), published in this issue of Gut 9.…”