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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.
- inflammatory bowel disease
- primary care
- gastroenterology
Data availability statement
No data are available. The THIN dataset cannot be shared under the data sharing agreement with the University of Birmingham on behalf of IQVIA.
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Data availability statement
No data are available. The THIN dataset cannot be shared under the data sharing agreement with the University of Birmingham on behalf of IQVIA.
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Footnotes
Correction notice This article has been corrected since it first published. In this article the word "IMRD-UK" has been replaced by "THIN" in the title and throughout the article because the database did not change its name with the change in ownership of the database.
Contributors KF, ST-P, BHW, RR and AC designed the study. RR extracted the data from THIN and created the datasets. KF, ST-P and BHW carried out the analysis. KF, BHW, ST-P and AC contributed to the interpretation of the findings. KF drafted the manuscript. All authors critically revised the manuscript and approved the final version. KF takes responsibility for the integrity and accuracy of the data analysis. KF acts as guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.
Funding KF is funded by a National Institute for Health Research (NIHR) DRF award (DRF-2016-09-038) for this research project. AC is supported by the National Institute for Health Research (NIHR) Applied Research Collaboration (ARC) West Midlands. This report presents independent research funded by the National Institute for Health Research (NIHR). The views expressed are those of the author and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care. The funder had no role in the study design, data collection, data analysis and interpretation, writing of the report or the decision to submit for publication.
Competing interests All authors have completed the Unified Competing Interest form (available on request from the corresponding author) and declare the following: KF is funded by the NIHR through a doctoral research fellowship. ST-P reports grants from the NIHR fellowship for Karoline Freemen. AC is supported by the NIHR ARC West Midlands initiative. BHW received grants from the Medical Research Council. RR has no conflicts to declare.
Provenance and peer review Not commissioned; externally peer reviewed.
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