Fecal calprotectin, intestinal ultrasound, and their combination for the diagnosis of inflammatory bowel disease

Abstract

Background: We aimed to evaluate the diagnostic accuracy of fecal calprotectin (FC) and intestinal ultrasound (IUS), independently and in combination, as screening tools for adults with suspected IBD to reduce the number of unnecessary endoscopic procedures.

Methods: We conducted a retrospective monocentric study that included consecutive adult patients with (i) ileocolonoscopy for suspected IBD between January 2021 and June 2023 who had either (ii) IUS and/or (iii) a FC test within 6 weeks. Bowel wall thickness (BWT) and the color Doppler signal (CDS) were evaluated for all segments. The presence of lymphadenopathy, loss of stratification, stricture, and fistula were also recorded.

Results: In total, 119 patients with a median age of 32 years (IQR, 24.0-41.0) were included. The most common symptoms were abdominal pain (n = 88, 75 %) and chronic diarrhea (n = 89, 75 %). Among the 119 patients, 74 (62 %) had IUS, 101 (82 %) had a FC test, and 56 (47 %) had both. Forty patients (34 %) had a diagnosis of IBD, including 31 (26 %) with CD and 9 (8 %) with UC. By ROC curve analysis, the best threshold of FC to diagnose IBD was 117 ug/g (Se 97 %, Sp 73 %, PPV 67 %, NPV 98 %, AUC 0.88, 95 %CI [0.81; 0.94], p = 0.006). Using this threshold, only 3 % of patients were misclassified as non-IBD. Screening by measuring FC levels would result in a 48 % reduction in the number of adults requiring endoscopy. Abnomal IUS was significantly associated with a diagnosis of IBD (OR 5.6, 95 %IC [2.1;16.2], P = 0.0008). The association of a BWT>3 mm and a positive CDS was associated with a Se, Sp, PPV, and NPV of 48 %, 100 %, 100 %, and 75 %, respectively, but 52 % of patients were misclassified as non-IBD. The combination of a BWT>3 mm, CDS, and FC>117 ug/g had a Se, Sp, PPV, and NPV of 44 %, 100 %, 100 %, and 69 %, respectively. For patients with a normal IUS and FC<117 ug/g, 4 % were misclassified as non-IBD.

Conclusions: The combination of FC and IUS is a useful screening strategy to identify patients who truly require endoscopy for suspected IBD. Calprotectin is a highly effective test for ruling out IBD. Conversely, relying solely on IUS lacks the discriminative power to safely rule out IBD. However, it shows a high PPV and is a potent tool for diagnosing IBD.

Keywords: Crohn's disease; Inflammatory bowel disease; Intestinal ultrasound and calprotectin.