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Test accuracy of faecal calprotectin for inflammatory bowel disease in UK primary care : a retrospective cohort study of the IMRD-UK data

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Freeman, Karoline, Taylor-Phillips, Sian, Willis, Brian H., Ryan, Ronan and Clarke, Aileen (2021) Test accuracy of faecal calprotectin for inflammatory bowel disease in UK primary care : a retrospective cohort study of the IMRD-UK data. BMJ Open, 11 (2). e044177. doi:10.1136/bmjopen-2020-044177

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Official URL: http://dx.doi.org/10.1136/bmjopen-2020-044177

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Abstract

Objective: To estimate the test accuracy of faecal calprotectin (FC) for inflammatory bowel disease (IBD) in the primary care setting using routine electronic health records.

Design: Retrospective cohort test accuracy study.

Setting: UK primary care.

Participants: 5970 patients (≥18 years) without a previous IBD diagnosis and with a first FC test between 1 January 2006 and 31 December 2016. We excluded multiple tests and tests without numeric results in units of µg/g.

Intervention: FC testing for the diagnosis of IBD. Disease status was confirmed by a recorded diagnostic code and/or a drug code of an IBD-specific medication at three time points after the FC test date.

Main outcome measures: Sensitivity, specificity, and positive and negative predictive values for the differential of IBD versus non-IBD and IBD versus irritable bowel syndrome (IBS) at the 50 and 100 µg/g thresholds.

Results: 5970 patients met the inclusion criteria and had at least 6 months of follow-up data after FC testing. 1897 had an IBS diagnosis, 208 had an IBD diagnosis, 31 had a colorectal cancer diagnosis, 80 had more than one diagnosis and 3754 had no subsequent diagnosis. Sensitivity, specificity, and positive and negative predictive values were 92.9% (88.6% to 95.6%), 61.5% (60.2% to 62.7%), 8.1% (7.1% to 9.2%) and 99.6% (99.3% to 99.7%), respectively, at the threshold of 50 µg/g. Raising the threshold to 100 µg/g missed less than 7% additional IBD cases. Longer follow-up had no effect on test accuracy. Overall, uncertainty was greater for specificity than sensitivity. General practitioners’ (GPs’) referral decisions did not follow the anticipated clinical pathways in national guidance.

Conclusions: GPs can be confident in excluding IBD on the basis of a negative FC test in a population with low pretest risk but should interpret a positive test with caution. The applicability of national guidance to general practice needs to be improved.

Item Type: Journal Article
Subjects: R Medicine > RA Public aspects of medicine
R Medicine > RC Internal medicine
Divisions: Faculty of Medicine > Warwick Medical School > Health Sciences
Faculty of Medicine > Warwick Medical School
Library of Congress Subject Headings (LCSH): Inflammatory bowel diseases , Inflammatory bowel diseases -- Immunological aspects, Inflammatory bowel diseases -- Treatment, Feces -- Analysis, Feces -- Examination
Journal or Publication Title: BMJ Open
Publisher: BMJ
ISSN: 2044-6055
Official Date: 22 February 2021
Dates:
DateEvent
22 February 2021Published
22 February 2021Available
8 February 2021Accepted
Volume: 11
Number: 2
Article Number: e044177
DOI: 10.1136/bmjopen-2020-044177
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Open Access
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
DRF-2016-09-038[NIHR] National Institute for Health Researchhttp://dx.doi.org/10.13039/501100000272

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