Review for 10.1186/s12876-016-0446-z (2016)

Reviewer’s report 
Title:  Faecal short-chain fatty acids - a diagnostic biom arker for irritable bowel syndrome? 
 
Version:  0 Date:  13 Oct 2015 
 
Reviewer:  Ulrike von-Arnim 
 
Reviewer's report: 
This is a case control study on how propionic/butyr ic acid ratio and propionic- butyric acid 
difference might serve as a possible biomarker for IBS- diagnose without performing an 
extensive diagnsotic work up. Specific and sensitiv e IBS- biomarkers are indeed a diagnsotic 
tool, which is warranted and could help to reduce c osts for extensive and expensive non- 
invasive and invasive exmaninations.  
 
Methods.  
Participants.  
In the depression and neurological group organic di seases were excluded. What kind of 
investigations were performed? In my understanding a neurological diagnostic work up was 
implemented to exclude orgnaic neurological disease s.  
IBS patients werde recruited from the above mention ed groups. The diagnosis IBS requires the 
exclusion of underlying organic or structural disea se of the GI tract. Please clarify how the 
diagnose IBS was made and how other diseases of the  GI tract were excluded (for example. 
IBS diarrhea: an important differential diagnosis i s microscopic colitis, how was this excluded? 
IBS Constipation: colonic cancer is an importatn di fferential diagnosis). How was control 
group recruited and what criteria were used to sele ct them (only negative Rome III criteria?. 
Goldstandard for control group are patients present ing for screening colonoscopy. 
Since it is well known that gut microbiom is influe nced by dietary habits and use of antibiotics, 
a truncated food frequency survey (e.g. vegetable i ntake/days per week) and history of 
antibiotic therapy needs to be recorded. Further it  is known, that the microbiota can differ 
depending on the race and /or ethnic background. Pl ease provide information about racial/ 
ethnic group of the participants and the control gr oup.  
Results.  
In table 2 neither propionic acid in mmol/l nor pro pionic acid in  molar % was significantly 
different in the two gruops. Propionic acid molar %  showed a trend towards significancy. Why 
did you chose propionic acid concentration as minue nd and dividend? Why didn´t you use 
butyric acid molar % (significant) and propionic ac id molar% calculating substraction? 
Addition would also leed to results, which may have  an intrinsic value. The idea and the reason 
for chosing these parameters needs further explanat ion and clarification. 
Table 2. Seen individually Butyric acid (mmol/l) an d propionic acid (mmol/l)were insignificant 
parameters, the calculated quotient is a significan t value, the idea behind this calculation needs 
further explanation.  
How is it possible to create a ROC curve using two insignificant parameters (Propionic acid 
and butyric acid mmol/l, which when using substract ion resulting in a significant difference? 
This operating and calculating prodedure needs clar ification.  
ROC curve: There are two Roc curves within the manu script. One curve is without lettering 
and legend. 
 
Discussion. This part of the manucript needs more f ocussing on the study it self and comparison 
to other studies with different reuslts concerning SCFA concentrations and amounts 
and also the different rates of butyric and propion ic acid. Futher the  pronounciation 
of theses two SCFA has to be explained and underlin ed by their possibly positive 
effects in the gut microbiom. 
 
Are the methods appropriate and well described? 
If not, please specify what is required in your com ments to the authors. 
No 
Does the work include the necessary controls? 
If not, please specify which controls are required in your comments to the authors. 
No 
 
 
Are the conclusions drawn adequately supported by t he data shown? 
If not, please explain in your comments to the auth ors. 
No 
Are you able to assess any statistics in the manusc ript or would you recommend an 
additional statistical review? 
If an additional statistical review is recommended,  please specify what aspects require further 
assessment in your comments to the editors. 
I am able to assess the statistics 
Quality of written English 
Please indicate the quality of language in the manu script: 
Acceptable 
Declaration of competing interests 
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