Yield of colorectal cancer at colonoscopy according to faecal haemoglobin concentration in symptomatic patients referred from primary care.

BACKGROUND: Lower gastrointestinal (GI) symptoms are poor predictors of colorectal cancer (CRC). This study examined the diagnostic yield of colonoscopy by faecal haemoglobin concentration (f-Hb) in symptomatic patients assessed in primary care by faecal immunochemical testing (FIT). METHODS: In three Scottish NHS Boards, FIT kits (HM-JACKarc, Hitachi Chemical Diagnostics Systems Co., Ltd, Tokyo, Japan) were used by GPs to guide referrals for patients with lower GI symptoms (lab data studied for 12 months from December 2015 onward in Tayside, 18 months from June 2018 onward in Fife, and 5 months from September 2018 onward in Greater Glasgow and Clyde). CRC cases diagnosed at colonoscopy were ascertained from colonoscopy and pathology records. RESULTS: 4841 symptomatic patients who underwent colonoscopy after FIT submission were included. Of 2166 patients (44.7%) with f-Hb <10 µg Hb/g faeces (µg/g), 14 (0.6%) were diagnosed with CRC, with a number needed to scope (NNS) of 155. Of 2675 patients (55.3%) with f-Hb ≥10 µg/g, 252 were diagnosed with CRC (9.4%) with a NNS of 11. Of 705 patients with f-Hb ≥400 µg/g, 158 (22.4%) were diagnosed with CRC with a NNS of 5. Over half of those diagnosed with CRC with f-Hb <10 µg/g had co-existing anaemia. CONCLUSIONS: Symptomatic patients with f-Hb ≥10 µg/g should undergo further investigation for CRC, while higher f-Hb could be used to triage its urgency during the COVID-19 recovery phase. Patients with f-Hb <10 µg/g, without anaemia, are very unlikely to be diagnosed with CRC and the majority need no further investigation.