Introduction: A large proportion of small bowel lesions in Crohn's disease (CD) may exist beyond the reach of ileocolonoscopy and there is no gold standard imaging modality to screen them, suggesting the need for optimal biomarkers. We aimed to compare the usefulness of C-reactive protein (CRP), faecal calprotectin (FC), and leucine-rich alpha-2 glycoprotein (LRG) in determining small bowel lesions of CD., Methods: This was a cross-sectional observational study. CRP, FC, and LRG were prospectively measured in patients with quiescent CD who underwent imaging examinations (capsule or balloon-assisted endoscopy, magnetic resonance enterography, or intestinal ultrasound) selected by the physician in clinical practice. Mucosal healing (MH) of the small bowel was defined as a lack of ulcers. Patients with a CD activity index >150 and active colonic lesions were excluded., Results: A total of 65 patients (27, MH; 38, small bowel inflammation) were analysed. The area under the curve (AUC) of CRP, FC, and LRG was 0.74 (95% confidence interval: 0.61-0.87), 0.69 (0.52-0.81), and 0.77 (0.59-0.85), respectively. The AUC of FC and LRG in a subgroup of 61 patients with CRP <3 mg/L (26, MH; 32, small bowel inflammation) was 0.68 (0.50-0.81) and 0.74 (0.54-0.84), respectively. The cut-off of 16 μg/mL of LRG showed the highest positive predictive value of 1.00 with specificity of 1.00, while negative predictive value was highest (0.71) with sensitivity of 0.89 at the cut-off of 9 μg/mL., Conclusion: LRG can accurately detect and/or exclude the small bowel lesions with two cut-off values., Competing Interests: K.A. has an endowed chair from AbbVie, JIMRO, Zeria Pharmaceutical, KYORIN Pharmaceutical, Mochida Pharmaceutical, and EA Pharma. T.K. received lecture fees from Takeda Pharmaceutical Co., Ltd. Activaid, Alfresa Pharma Corporation, Zeria Pharmaceutical Co., Ltd., KYORIN Pharmaceutical Co., Ltd., Nippon Kayaku Co., Ltd., Mitsubishi Tanabe Pharma Corporation, AbbVie GK, Pfizer Japan Inc., Janssen Pharmaceutical K.K., Thermo Fisher Diagnostics K.K., and JIMRO Co., Ltd.; received research grants from AbbVie GK, Activaid, Alfresa Pharma Corporation, JMDC Inc., Gilead Sciences, Inc., Nippon Kayaku Co., Ltd., Eli Lilly Japan K.K., Mochida Pharmaceutical Co., Ltd., Janssen Pharmaceutical K.K., Pfizer Japan Inc., Takeda Pharmaceutical Co., Ltd., Ferring Pharmaceuticals, and Bristol Myers Squibb; received scholarship contributions from Mitsubishi Tanabe Pharma Corporation, Zeria Pharmaceutical Co., Ltd., and Nippon Kayaku Co., Ltd.; belonged to study group sponsorship by Otsuka Holdings, AbbVie GK, EA Pharma Co., Ltd., Zeria Pharmaceutical Co., Ltd., JIMRO Co., Ltd., KYORIN Pharmaceutical Co., Ltd., and Mochida Pharmaceutical Co., Ltd.; received advisory/consultancy fees from Janssen Pharmaceutical K.K., EA Pharma Co., Ltd., KISSEI Pharmaceutical Co., Ltd., Takeda Pharmaceutical Co., Ltd., Activaid, Pfizer Japan Inc., Nippon Kayaku Co., Ltd., Alfresa Pharma Corporation, KYORIN Pharmaceutical Co., Ltd., AbbVie GK, Mochida Pharmaceutical Co., Ltd, and Mitsubishi Tanabe Pharma Corporation. MN has served as a speaker or a consultant in Covidien, Mochida Pharmaceutical, Takeda Pharmaceutical, Zeria Pharmaceutical, KYORIN Pharmaceutical, and Nippon Kayaku and received research funding from Mitsubishi Tanabe Pharma and Japanese foundation for research and promotion of endoscopy. SS has served as a speaker for AbbVie, Takeda Pharmaceutical, Mitsubishi Tanabe Pharma, Nippon Kayaku, and Zeria Pharmaceutical and as an endowed chair for AbbVie, JIMRO, Zeria Pharmaceutical, KYORIN Pharmaceutical, Mochida Pharmaceutical, and EA Pharma. HM has received research grant from Takeda Pharmaceutical. YM has an endowed chair from AbbVie, JIMRO, Zeria Pharmaceutical, KYORIN Pharmaceutical, Mochida Pharmaceutical, and EA Pharma. TF has received research funding from Mitsubishi Tanabe Pharma. TH has received lecture fees from Aspen Japan K.K, AbbVie GK, Ferring, Gilead Sciences, Janssen, JIMRO, Mitsubishi Tanabe Pharma, Mochida Pharmaceutical, Pfizer, and Takeda Pharmaceutical; advisory/consultancy fees from APO PLUS Station, AbbVie GK, Bristol Myers Squibb, Celltrion, EA Pharma, Eli Lilly, Gilead Sciences, Janssen, KYORIN, Mitsubishi Tanabe Pharma, Nichi-Iko Pharmaceutical, Pfizer, Takeda Pharmaceutical, Zeria Pharmaceutical and research grants from AbbVie GK, Activaid, Alfresa Pharma Corporation, JMDC Inc., Gilead Sciences, Inc., Nippon Kayaku Co., Ltd., Eli Lilly Japan K.K., Mochida Pharmaceutical Co., Ltd., Janssen Pharmaceutical K.K., Pfizer Japan Inc., Takeda Pharmaceutical Co., Ltd., Ferring Pharmaceuticals, and Bristol Myers Squibb; received scholarship contributions from Mitsubishi Tanabe Pharma Corporation, Zeria Pharmaceutical Co., Ltd., Nippon Kayaku Co., Ltd.; and belonged to study group sponsorship by Otsuka Holdings, AbbVie GK, EA Pharma Co., Ltd., Zeria Pharmaceutical Co., Ltd., JIMRO Co., Ltd., KYORIN Pharmaceutical Co., Ltd., and Mochida Pharmaceutical Co., Ltd., (© 2023 The Author(s). Published by S. Karger AG, Basel.)