·To investigate the values of fecal calprotectin (FC), C-reactive protein (CRP) and interleukin 6 (IL-6) in diagnosing the gastrointestinal mucosal injury in the patients with Crohn′s disease (CD).

·A total of 52 CD patients admitted to Renji Hospital, Shanghai Jiao Tong University School of Medicine from June 2019 to June 2020 were enrolled in the study. The patients were divided into uninjured mucosa group and injured mucosa group based on the gastrointestinal endoscopic results, and the clinical features of the two groups were compared. The level of IL-6 was detected by cytometric bead array. The content of FC was detected by immunofluorescence chromatography. CRP in the whole blood was detected by nephelometry. IL-6 and CRP were detected within 24 h of admission, while FC was detected within 72 h. The results were compared between the two groups. The independent influence factors of mucosal injury were analyzed by multivariate Logistic regression. The receiver operating characteristic (ROC) curve was used to determine the values of IL-6, CRP, FC and their combination in judging mucosal injury.

·Among the 52 patients, there were 21 patients in the uninjured mucosa group and 31 in the injured mucosa group. There were no significant differences in the age and gender between the two groups. The significant difference was only identified in the distribution of disease behavior in the Montreal Classification (P<0.05). The levels of IL-6, CRP and FC in the injured mucosa group were 11.1 (3.67, 17.54) pg/mL, 8.02 (2.13, 30.96) mg/L and 448.4 (212.90, 639.50) μg/g, respectively, which were significantly higher than those in the uninjured mucosa group (P<0.05). Logistic regression analysis suggested that only FC was an independent factor for judging the injured status of gastrointestinal mucosa in the CD patients (OR=1.006, P<0.05). The areas under the ROC curves (AUCs) of IL-6, CRP and FC for judging the state of gastrointestinal mucosal injury were 0.71, 0.88 and 0.85, respectively (all P<0.05). The AUCs of FC+CRP and FC+IL-6 were 0.91 and 0.84, respectively (both P<0.05). The AUC of FC+IL-6+CRP was 0.92 (P<0.05). By comparing the ROC curves of the two-item combined detection and the three-item combined detection, no significant difference could be identified in the AUC between FC+CRP and FC+IL-6+CRP. However, a significant difference was identified between FC+IL-6 and FC+IL-6+CRP (P=0.045). Meanwhile, the sensitivities and specificities of both FC+CRP and FC+IL-6+CRP were 77% and 100%, respectively.

·The combined detection of FC and CRP, as well as the combined detection of FC, IL-6 and CRP, can effectively judge the gastrointestinal mucosal injury in patients with CD, the diagnostic values of which are similar; based on the simplicity and the cost, the combined detection of FC and CRP is more recommended clinically.