Review for 10.1186/s12876-019-1135-5 (2019)

Reviewer ’s report  
 
Title: Appraisal of the faecal haemoglobin, age and sex tes t (FAST) score in assessment of 
patients with lower bowel symptoms: An observationa l study  
 
Version: 1 Date: 12 Aug 2019  
 
Reviewer: Jennifer Cooper  
 
Reviewer's rep ort: 
-I was not a reviewer of the previous iteration of this submitted paper so apologies for any repeat 
observations which have been subsequently addressed.  
 
-This is not a classical prediction model validation stud y (this requires discrimination and 
calibration compared to development study) instead as the authors describe it is an evaluation of 
the FAST score in patients with lower bowel symptoms using data from an NHS board in 
Scotland. The paper provides timely d ata and outcomes on what is a very much growing area 
relating to risk prediction and FIT in symptomatic patients. The aim is to look at the 'added 
value' of the FAST score. More specifically - to perform an initial evaluation of the utility of the 
FAST sco re in patients presenting in primary care for investigation of lower bowel symptoms, in 
one region of Scotland, over the first year of routine use of FIT.  
-The model does not provide individualised probabilities as it is a logistic regression model 
applie d without the intercept (the beta coefficient components are used to generate a linear 
predictor and thus score). If possible, this needs to be specified in this paper so the reader knows 
that the model was originally developed using logistic regression an d that the score is generated 
using the linear predictor (maybe mention the original intercept for information).  
-A further suggestion would be to provide a study flow diagram as I was not always clear on 
where the numbers for Group A and Group B were de rived from (include FAST score/ FIT 
cutoff and CRC/SBD outcomes). I appreciate that the study uses routine data, but the authors 
could expand upon how the selective nature of the population will likely affect the risk 
scoring/performance (or utility).  
-Describe in the methods where the cut -off of 2.12 is derived for the FAST score (this may be in 
original development paper, i.e. based on 99% sensitivity but is an important consideration when 
assessing performance). Using a cutoff which maximises sensitivit y does not always reflect 
clinical reality and can inflate performance measures (STARD guidelines)  
 
-An area which may require attention is the use of different analytical systems (brands of FIT for 
example) for derivation compared to validation studies an d then also assigning the same 
grouping cut -offs for the different FITs used. The prediction model was developed using the OC -
Sensor which would have different diagnostic accuracy to the HM -JACKarc - this would 
subsequently affect performance of the predic tion tool. Using a different test can essentially 
make this a different predictor in the model to the one used for model development. For a 
diagnostic accuracy study for example this would affect outcomes such as sensitivity and 
specificity. This is briefl y addressed in the discussion (and the validation of the model used 
multiple analytical systems) but I think could potentially warrant more discussion on the 
resultant affects on predictive performance/results.  
-Consider that the covariate pattern which p redicts CRC may be different to the pattern which 
predicts other bowel diseases and would thus affect performance and perhaps selection of the 
score cut -off.  
 
Small edits:  
Typos  
 
-Under Background  
line 23/24 "symptoms have be well documented…"  
 
-Under M ethods  
Line 7/8  
"The reports also sign -posted GP"  
 
-Under Discussion  
Line 7  
The confidence interval does not match up to the sensitivity of 73.7% (95% CI: 95.9 -98.9)  
 
 
 
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the author s. 
 
Yes 
 
Are the conclusions drawn adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
Yes 
 
Are you able to assess any statistics in the manus cript or would you recommend an 
additional statistical review?  
If an additional statistical review is recommended, please speci fy 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 qualit y of language in the manuscript:  
 
Acceptable  
 
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 financial ly from the publication of this 
manuscript, either now or in the future?  
 
2. Do you hold any stocks or shares  in an organisation t hat 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?  
 
4. Have you recei ved reimbursements, fees, funding, or salary from an organization that 
holds or has applied for patents relating to the content of the manuscript?  
 
5. Do you have any other financial competing interests?  
 
6. Do you have any non -financial competing interests in relation to this paper?  
 
 
 
 
If you can answer no to all of the above, write 'I declare that I have no competing interests' 
below.  If your reply is yes to any, please give details below.  
 
I declare that I have no competing interests  
 
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