Review for 10.1186/s12876-021-02042-7 (2021)

Title: Outcomes from colonoscopy following referral from New Zealand general practice: a
retrospective analysis
Version: 1 Date: 06 Oct 2021
Reviewer:  Keith Siau
Reviewer's report:
This study by Lawrenson et al was a retrospective evaluation of colonoscopy practice in primary
care referrals to gastroenterology and surgical departments within a single district hospital in
Waitemata, New Zealand. The authors aimed to study the proportion of patients who underwent
colonoscopy, factors associated with colonoscopy, rates of colorectal cancer (CRC) and factors
associated with CRC. A registry-linkage study (combining primary care and national cancer
registries) was conducted over a 2 year period before COVID-19, and seemingly before the
implementation of faecal immunohistochemical testing. The authors found that nearly 1/3rd of
patients underwent colonoscopy, of whom 5.5% had CRC. Multivariable analyses (which appear
valid) were done to identify factors associated with these outcomes. The authors conclude that
patients who have a high suspicion of CRC (HSCan) flagged by primary care have a high risk
of CRC and should not be re-triaged by hospital practitioners. Despite my concerns (see below),
there is merit in the study as it is reasonably sized (6718 colonoscopies with 372 CRC cases),
the statistical approach seems valid and that such data from New Zealand are lacking. Most
importantly, the findings may help to prevent delays in the diagnostic pathway in patients which
high GP suspicion of CRC.
My comments are attached:
1. These data are interesting, but there are also inherent weaknesses with the methodology,
notably the lack of analysis in relation to patient symptoms (e.g. diarrhoea, bleeding, rectal
mass, positive guiaic/FIT, iron deficiency anaemia, etc). Although these factors are presumably
included under the HSCan variable, this is impossible to disentangle.
2. Another limitation is that such data are also likely to be outdated and no longer representative
in light of COVID-19. In fact, COVID-19 has not been mentioned in the manuscript at all. This
should be discussed as COVID-19 has affected endoscopy practices (and triaging) worldwide.
3. I am somewhat confused why such a high number of patients (1 in 3) of those over 30
year old underwent colonoscopy, considering that a significant proportion of referrals to GI
departments would have isolated upper GI symptoms only. How does this proportion compare
to other settings?
4. What proportion of patients were referred with positive FIT? Was this used as a triage tool?
There is now good evidence to support FIT in the risk stratification of symptomatic patients.
5. What is the correlation between GP HSCan and Hospital HSCan? What percentage of referrals
with high GP HSCan were downgraded? Do you also have data on prioritisation of colonoscopy,
i.e. time from referral to investigation?
6. For readers who are unfamiliar with the New Zealand healthcare system, it would be helpful
if this could be described, i.e. who pays for colonoscopy? Out-of-pocket expenses may explain
the variation in colonoscopy between Maori and non-Maori populations.
7. Are there data on colonoscopy non-attendance? What was the rate and did this vary between
Maori and non-Maori populations?
Thank you for your thoughtful submission and for considering my comments.