Bilirubin statistically accounts for the association between Enterobacterales lineage and Mayo endoscopic score in ulcerative colitis: a cross-sectional associational variable analysis

BackgroundPatients with ulcerative colitis (UC) frequently exhibit gut enrichment of Enterobacteriaceae and reduced serum bilirubin levels. However, whether bilirubin statistically accounts for the association between Enterobacteriaceae abundance and UC disease activity remains unclear.MethodsThis study enrolled 81 UC patients. The relative abundances of Enterobacterales lineage (Gammaproteobacteria, Enterobacterales, Enterobacteriaceae, and Escherichia-Shigella) were determined by 16S rRNA sequencing, and disease activity was assessed using the Mayo endoscopic score (MES). Total bilirubin (TBIL) and indirect bilirubin (IBIL) were examined as potential associative variables. Associational variable analyses were performed using bootstrap methods with 5,000 resamples, and sensitivity analyses were conducted after adjusting for covariates.ResultsThe abundances of Enterobacterales lineage were positively correlated with MES (p = 0.34–0.40) and negatively correlated with TBIL and IBIL (p = −0.31 to −0.48). Associational variable analyses showed that bilirubin significantly and partially accounted for these positive associations. In covariate-adjusted models, the associational proportions ranged from 40.8% to 42.3% for TBIL and from 37.2% to 40.0% for IBIL.ConclusionBilirubin statistically accounts for approximately 37.2%–42.3% of the association between Enterobacterales lineage abundance and UC disease activity. Owing to the cross-sectional design, these findings reflect statistical covariation rather than causal effects, and prospective studies are needed to establish temporal direction.