Review for 10.1186/s12876-022-02191-3 (2022)

Reviewer’s report
Title: 
Characterization of short-chain fatty acids in patients with ulcerative
colitis: a meta-analysis
Version: 
0 
Date: 
02 Feb 2022
Reviewer's report:
Dear authors, I read with interest your manuscript entitled "Characterization of
short-chain fatty
acids in patients with ulcerative colitis: a meta-analysis"
I have major concerns. Please find attached my comments below.
1. All included studies are case-control studies, some of them with a small
sample size,
possibly overestimating reported findings. This is a major limitation of this meta-
analysis.
2. The study has several major biases, some of which have also been
acknowledge by the
authors:
a) Among included studies, the parameter 'disease extent' was assessed based on
highly
heterogeneous standards: some studies exclusively considered laboratory
findings, some
clinical findings, others endoscopy findings. This leads to high risk of selection
bias
regarding the dosage of SCFAs, as patients included in one study may well have
diseases with different grades of severity and extent.
b) In Table 1 the authors are reporting on ulcerative colitis; however, there are 2
studies in
which CDAI and PCDAI scores were calculated. This may be incorrect as CDAI
and
PCDAI scores are used in Crohn's disease and not UC.
c) Data regarding the severity of UC is missing. This is relevant as patients with
Mayo 2-3
colitis may have greater alterations of the mucosa and, theoretically, lower levels
of
SCFAs.
d) The authors did not report what was the criteria for defining remission:
clinical? Mucosa
healing? Based on these parameters, different considerations could be drawn.
Indeed,
those who experienced mucosal healing could possibly have levels of SCFAs
comparable to those of the general population.
e) Different laboratory tests were used for the dosages of SCFAs in different
studies.
Accordingly, this would greatly bias the results of the meta-analysis, strongly
limiting its
clinical relevance.
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Declaration of competing interests
Please complete a declaration of competing
interests, considering the following questions:
1
. 
Have you in the past five years received reimbursements, fees, funding, or
salary from an organisation that may in any way gain or lose financially
from the publication of this manuscript, either now or in the future?
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. 
Do you hold any stocks or shares in an organisation that may in any way
gain or lose financially from the publication of this manuscript, either now
or in the future?
3
. 
Do you hold or are you currently applying for any patents relating to the
content of the manuscript?
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Have you received reimbursements, fees, funding, or salary from an
organization that holds or has applied for patents relating to the content of
the manuscript?
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. 
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paper?
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interests' below. If your reply is yes to any, please give details below.
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
Yes
Are the methods sufficiently described to allow the study to be repeated?
Yes
Is the use of statistics and treatment of uncertainties appropriate?
Yes
Is the presentation of the work clear?
No
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes