Urgent suspected cancer referral decision could be informed by fit thresholds tailored to age and anaemia status

Introduction NICE guidelines outline a risk threshold for urgent suspected cancer (USC) referral as a 3% positive predictive value and recommend use of faecal immunochemical tests (FIT) at a cut-off of ≥10 µg Hb/g faeces, along with clinical acumen, as a rule-out test for colorectal cancer (CRC).1 2 Data from Nottingham has concluded that faecal haemoglobin (f-Hb) cut-offs could be tailored to maintain a 3% CRC risk according to age and anaemia status.3 We aimed to assess whether this could be replicated in patients presenting to primary care in NHS Tayside with new bowel symptoms.

Methods We conducted a retrospective single-centre observational study of patients who submitted a FIT between December 2015-December 2019: f-Hb was estimated using HM-JACKarc (Hitachi Chemical Diagnostics Systems). Incident CRC were identified via record linkage to the Scottish Cancer Registry with a homogenous follow-up time of two years. Kaplan-Meier estimates were used to determine cumulative one-year CRC risk.

Results Of 34353 samples with a valid f-Hb result, 7831 (22.8%) had f-Hb ≥10µg Hb/g. 1831 (23.4%) were in the 10–19 µg Hb/g range in which 22 (1.2%) had CRC. Overall, 521 incident CRC were recorded. Cumulative one-year CRC risk was determined by age and by f-Hb result; it was >3% in all patients aged >40 years with f-Hb ≥100µg Hb/g, and in patients >55 years with f-Hb ≥40µg Hb/g and in patients >85 years with f-Hb ≥20µg Hb/g. The presence of iron-deficiency anaemia (IDA) lowered the > 3% CRC risk threshold to ≥10µg Hb/g only in patients >70 years.

Conclusions In primary care, incidence of CRC in patients with f-Hb of 10–19 µg Hb/g is very low. Furthermore, our results support the proposal that USC referral decision could be informed by f-Hb thresholds tailored to age and IDA status to direct colonoscopy resource towards those at highest risk.