When faecal immunochemical test (FIT) was introduced in 2017, there was little evidence on the clinical implications of using FIT to triage patients with low-risk symptoms of possible colorectal cancer in primary care.
In a new study, published in the British Journal of Cancer, data from all health care providers in the South West of England was used to identify 3890 patients aged ≥50 years presenting to primary care with low-risk symptoms of colorectal cancer who had a FIT between 1 June 2018 and 31 December 2018. A threshold of 10 μg Hb/g faeces defined a positive test.
A total of 618 (15.9%) patients tested positive. Of these, 458 (74.1%) had an urgent referral to specialist lower gastrointestinal services within three months and 43 were diagnosed with colorectal cancer within 12 months.
Of the 3272 who tested negative, 324 (9.9%) had an urgent referral within three months and eight were diagnosed with colorectal cancer within 12 months.
The positive predictive value for FIT was 7.0 per cent (95% CI, 5.1%-9.3%). The negative predictive value was 99.8 per cent (CI, 99.5%-99.9%). Sensitivity was 84.3 per cent (CI, 71.4%-93.0%), whereas specificity was 85.0 per cent (CI, 83.8%-86.1%).
The results showed that a threshold of 37 μg Hb/g faeces would identify patients with an individual 3 per cent risk of cancer.
Other cancers were also diagnosed, including 16 cases of oesophago-gastric or pancreatic cancer, of whom only four had a FIT result over the threshold. The authors say this suggests that GPs should consider other intra-abdominal cancers in patients with f-Hb