'Low' faecal immunochemical test (FIT) colorectal cancer: a 4-year comparison of the Nottingham '4F' protocol with...

The aim of this work was to evaluate colorectal cancer (CRC) outcomes after 'low' (sub-threshold) faecal immunochemical test (FIT) results in symptomatic patients tested in primary care.

This work comprised a retrospective audit of 35 289 patients with FIT results who had consulted their general practitioner with lower gastrointestinal symptoms and had subsequent CRC diagnoses. The Rapid Colorectal Cancer Diagnosis pathway was introduced in November 2017 to allow incorporation of FIT into clinical practice. The local '4F' protocol combined FIT results with blood tests and digital rectal examination (DRE): FIT, full blood count, ferritin and finger [DRE]. The outcome used was detection rates of CRC, missed CRC and time to diagnosis in local 4F protocols for patients with a subthreshold faecal haemoglobin (fHb) result compared with thresholds of 10 and 20 μg Hb/g faeces.

A single threshold of 10 μg Hb/g faeces identifies a population in whom the risk of CRC is 0.2%, but this would have missed 63 (10.5%) of 599 CRCs in this population. The Nottingham 4F protocol would have missed fewer CRCs [42 of 599 (7%)] despite using a threshold of 20 μg Hb/g faeces for patients with normal blood tests. Subthreshold FIT results in patients subsequently diagnosed with a palpable rectal tumour yielded the longest delays in diagnosis.

A combination of FIT with blood results and DRE (the 4F protocol) reduced the risk of missed or delayed diagnosis. Further studies on the impact of such protocols on the diagnostic accuracy of FIT are expected. The value of adding blood tests to FIT may be restricted to specific parts of the fHb results spectrum.