Plasma <scp>Immunoglobulin A</scp> and intestinal ultrasound: Novel indicators for disease activity monitoring in inflammatory bowel disease—Insights from a Taiwan cohort

Abstract Intestinal ultrasound (IUS) is a non‐invasive imaging method used to evaluate bowel wall inflammation and monitor disease activity in inflammatory bowel disease (IBD) patients. Both the European Crohn's and Colitis Organization and the American Gastroenterological Association endorse IUS for monitoring disease activity and identifying complications at the point of care. However, to date, no published data are available regarding the use of IUS for IBD management in Taiwan. Similar to the specificity of IUS in visualizing gut inflammation, immunoglobulin A (IgA) is a key immunoglobulin central to gut mucosal immunity. Recent studies have explored the involvement of IgA in IBD, but the relationship between IgA levels and bowel wall inflammation was unknown. We enrolled 28 IBD patients, including 19 with ulcerative colitis (UC) and 9 with Crohn's disease (CD), from the outpatient clinic of China Medical University Medical Center. All patients underwent IUS between July 2023 and August 2024. Ultrasound scores were based on the Milan ultrasound criteria (MUC) for UC and the bowel ultrasound score (BUSS) for CD. Plasma levels of erythrocyte sedimentation rate, C‐reactive protein (CRP), albumin, IgA, partial Mayo score, and Crohn's disease activity index (CDAI) were collected at baseline, during treatment, and after 52 weeks of advanced therapy (Adalimumab, Vedolizumab, or Tofacitinib). IUS findings were closely correlated with disease activity. In UC, the MUC score was positively correlated with CRP ( R 2 = 0.4888, p &lt; .0001), partial Mayo score ( R 2 = 0.3652, p = .0002), and negatively with albumin levels ( R 2 = 0.3747, p = .0002). In CD, the BUSS score showed a positive correlation with CDAI ( R 2 = 0.2694, p = .0394). Plasma IgA levels were significantly associated with bowel wall thickness (BWT) in both UC and CD ( R 2 = 0.1759, p = .0041). Furthermore, plasma IgA was strongly correlated with the BUSS score ( R 2 = 0.6585, p = .0001) in CD patients. Notably, when BWT exceeded 3.5 mm, plasma IgA levels increased significantly ( p = .0025). These results demonstrate that IUS is an effective tool for monitoring disease activity and evaluating therapeutic responses in IBD patients. Besides, plasma IgA reflects the bowel wall inflammation, particularly in conjunction with IUS.