Review for 10.1186/s12876-021-01675-y (2021)

Reviewer’s report
Title: 
Diagnostic accuracy assessment of molecular prediction model for the risk
of NAFLD based on MRI-PDFF diagnosed Chinese Han population
Version: 
0 
Date: 
22 Aug 2020
Reviewer: 
Rajarshi Banerjee
Reviewer's report:
Overall, nice, well executed study comparing an existing algorithm for assessing
likelihood of NAFLD with a new algorithm and benchmarking against NAFLD.
I congratulate the authors.
Introduction
Page 4
Line 17 - would be worthwhile referencing the superior performance of PDFF
measured with IDEAL (Hernando et al, Reeder group in Wisconsin) versus
simple PDFF. In reference 25, which appears in results, you use a specific PDFF
cutoff of 6.4% - this should be justified here.
Line 46 'In fact, the MRI-PDFF examination is expensive and the machine is
unattainable.' This needs referencing and context, as in US and EU MRI is cost-
effective versus other methods (Blake et al, BMJ Open 2016). As this is for the
Han population, approximate local pricing and ideally cost-effectiveness data
should be added, ideally in a couple of sentences contrasting them with the liver
biopsy diagnostic pathway. Access to MRI may be the biggest issue, more so
even than cost. Number of scanners per 100,000 people would be a useful
statistic.
https://bmjopen.bmj.com/content/bmjopen/6/9/e010507.full.pdf
Methods
Page 6 line 24
Participants with a MRI-PDFF value ≥ 6.4% was diagnosed as the NAFLD
patients [25]
Results
Youden Index - I think this is the correct approach
When presenting numbers/results, take care that they are not overly precise eg
only report BMI to one decimal place (page 7, line 34 'BMI value was
significant higher in the NAFLD group (28.25 ± 4.07) than in the health group
(25.14 ± 3.98) (P < 0.001)'). Likewise AUROC should be to 2 significant figures
only. 
I think the purpose of the model is to be sensitive to disease, so it would be
useful to have the cutoff which would have the same sensitivity (86% reported
by Kotronen), and report this from the AUROC curve. This would allow easier
comparison
Discussion
This is neatly written, but would benefit from three additional sentences/short
paragraghs for context. 
1. How is NAFLD thought to be different in the Han population?
2. How is current care delivered for suspected NAFLD in Qingdao?
3. How do the authors feel this molecular prediction model will be used?
Community assessment and then triaging for MRI? 
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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
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Yes
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes