BackgroundInflammatory bowel disease (IBD) is a chronic intestinal disorder characterized by recurrent flare-ups and remission. Leucine-rich α2-glycoprotein (LRG) has been developed as a new serum biomarker of disease activity in patients with IBD. However, there have been no reports on whether plasma LRG can be used as an alternative to serum LRG. Therefore, in this retrospective study, we evaluated the usefulness of plasma LRG compared to serum LRG.MethodsWe conducted a single-center retrospective observational study. A total of 108 IBD patients (ulcerative colitis [UC], 56; Crohn’s disease [CD], 52) who received treatment at Sapporo Medical University Hospital between August 2020 and September 2021 were enrolled. Serum and plasma LRG levels were measured using the NANOPIA LRG kit. Disease activity was assessed using the Crohn’s Disease Activity Index (CDAI) for CD and partial Mayo (pMayo) score for UC. Endoscopic activity was evaluated using the Mayo Endoscopic Subscore (MES) and Ulcerative Colitis Endoscopic Index of Severity (UCEIS) in patients with UC and the Simple Endoscopic Score for Crohn’s Disease (SES-CD) score in patients with CD.ResultsSerum LRG levels significantly correlated with plasma LRG levels (r= 0.990,p<0.0001). Plasma LRG levels were significantly associated with SES-CD (r= 0.992,p<0.0001), indicating that plasma LRG levels may predict endoscopic activity in CD. In UC patients, the cutoff values of plasma LRG for remission were 12.7 μg/mL for MES ≤1 and 10.0 μg/mL for UCEIS of = 0.ConclusionThe present study showed that plasma LRG levels correlate well with serum LRG levels. Therefore, plasma LRG can be clinically applied as a biomarker for assessing endoscopic disease activity in patients with IBD.