Faecal calprotectin for differentiating between irritable bowel syndrome and inflammatory bowel disease: a useful screen in daily gastroenterology practice

Abstract

Objective: To determine the best faecal calprotectin (FCP) cut-off level for differentiating between irritable bowel syndrome (IBS) and organic disease, particularly inflammatory bowel disease (IBD), in patients presenting with chronic diarrhoea.

Design: Retrospective analysis of patients who had colonoscopy, histology and FCP completed within 2 months.

Setting: District general hospital.

Patients: Consecutive new patients with chronic diarrhoea lasting longer than 4 weeks.

Interventions: Patients were seen by a single experienced gastroenterologist and listed for colonoscopy with histology. Laboratory investigations included a single faecal specimen for calprotectin assay (lower limit of detection: 8 µg/g), the results used for information only.

Main outcome measures: Six FCP cut-off levels (range 8-150 µg/g) were compared against the 'gold standard' of histology: inflammation 'present' or 'absent'.

Results: Of 119 patients studied, 98 had normal colonoscopy and histology. The sensitivity of FCP to detect IBD at cut-off levels 8, 25 and 50 µg/g was 100% (with corresponding specificity 51%, 51%, 60%). In contrast, the lowest FCP cut-off, 8 µg/g, had 100% sensitivity to detect colonic inflammation, irrespective of cause (with negative predictive value (NPV) 100%). Importantly, 50/119 patients (42%) with FCP <8 µg/g had normal colonoscopy and histology.

Conclusions: Our results suggest that using FCP to screen patients newly referred for chronic diarrhoea could exclude all without IBD and, at a lower cut-off, all without colonic inflammation, thus avoiding the need for colonoscopy. Such a major reduction has implications for resource allocation.

Keywords: CHRONIC DIARRHOEA; HISTOPATHOLOGY; IBD; IRRITABLE BOWEL SYNDROME; STOOL MARKERS.

Figure 1

Individual patients’ FCP (μg/g) values (n=119). IBS n=98, Crohn's disease n=6, UC n=6. ‘Others’ n=9 (note that the 5th value from the top represents two patients). ‘Others’=other organic diseases (FCP value). Two microscopic colitis (8, 50). One bacterial colitis (190). One infective (257). Four adenoma (40, 60, 63, 163). One adenocarcinoma (82). FCP, faecal calprotectin; IBS, irritable bowel syndrome; UC, ulcerative colitis.

Figure 2

distinguishing IBD versus D-IBS. FCP: Six cut-off levels were used ranging from 8 to 150 μg/g. Top: Paired forest plot. Bottom right: Table of diagnostic accuracy at each FCP cut-off level. Bottom left: SROC curve. Diagnostic accuracy at each FCP cut-off level and 95% confidence contours. Each of the six circles represents an FCP cut-off value ranging from 8 (No. 1) to 150 μg/g (No. 6). Note: Circle No. 2 is a fusion of Nos. 1 and 2 as these overlap. TP, true positive; FP, false positive; FN, false negative; TN, true negative; FCP, faecal calprotectin; IBD, inflammatory bowel disease; IBS, irritable bowel syndrome; SROC, summary receiver operating characteristic.

Figure 3

Distinguishing organic disease versus D-IBS. FCP: Six cut-off levels were used ranging from 8 to 150 μg/g. Top: Paired forest plot. Bottom right: Tables shows diagnostic accuracy at each FCP cut-off level. Bottom left: SROC curve. Diagnostic accuracy at each FCP cut-off level and 95% confidence contours. Each of the six circles represents an FCP cut-off value ranging from 8 (No. 1) to 150 μg/g (No. 6). TP, true positive; FP, false positive; FN, false negative; TN, true negative; FCP, faecal calprotectin; IBS, irritable bowel syndrome; SROC, summary receiver operating characteristic.