Comment on: Double faecal immunochemical testing in patients with symptoms suspicious of colorectal cancer

Dear Editor

We write regarding the recent paper by Gerrard et al.¹, which was recently discussed at ‘CRAMSURG’, an online journal club based in the UK (www.cramsurg.org).

We would like to congratulate the authors for their efforts in performing this study, especially during the COVID-19 pandemic. We discussed several issues that we would like to raise.

• Some included referrals (such as for abdominal pain, weight loss, or palpable rectal mass) would not always require endoluminal investigations. What was the rationale for including such patients?

• What definition of Iron deficiency anaemia (IDA) was adopted by the authors for the purpose of this study? How many cases of IDA were corroborated by the use of haematinics testing?

• Was there a reason to choose March 2020 as the starting point for recruitment in the double-faecal immunochemical test (FIT) cohort? The recruitment intervals for the single- and double-FIT cohorts were 14 and 17 months respectively; was there a reason to prolong recruitment for the second cohort?

• The two cohorts differ in terms of reasons for referral, with more cases of palpable abdominal or rectal mass in the double-FIT cohort. Could such differences be due to the COVID-19 pandemic? Could this have affected the results of the study?

• The authors highlight how CT colonography (CTC) was more commonly used in the double-FIT cohort. Given the inability to directly visualize mucosa or take biopsies, could the more widespread use of CTC have missed cases of inflammatory bowel disease?

• FITs perform better at detecting left rather than right colonic malignancies. Do the data from this study support this?

• Calculating likelihood ratios from the available data, adopting a double-testing strategy would reduce the negative likelihood ratio from 0.2 to 0.05—corroborating the fact that double testing would be a very good rule-out test.