CTI as a biomarker for diarrhea in U.S. adults: insights from NHANES 2005-2010.

Background: The C-Reactive protein-triglyceride-glucose index (CTI), a novel composite biomarker integrating inflammation and insulin resistance, has shown promise in predicting metabolic and inflammatory outcomes. However, its association with bowel dysfunction remains unexplored.

Methods: This population-based cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) 2005–2010 cycles. A total of 4,165 participants were included after rigorous exclusion criteria. CTI was calculated using the formula: 0.412 × Ln(CRP) + TyG, where TyG represents the triglyceride-glucose index. Diarrhea and constipation were defined based on the Bristol Stool Form Scale and bowel frequency. Logistic regressions were employed to assess associations between CTI and bowel dysfunction. Subgroup and mediation analyses were conducted to explore potential effect modifications and underlying mechanisms.

Results: Higher CTI levels were significantly associated with increased diarrhea risk (adjusted OR = 1.58, 95% CI: 1.20–2.10,  < 0.05), with a dose–response relationship observed across CTI quartiles ( for trend = 0.047). No significant association was found between CTI and constipation ( > 0.05). Subgroup analyses revealed consistent associations across most demographic and clinical characteristics, with no significant interaction effects (all for interaction > 0.05). Mediation analysis revealed that body mass index (BMI), waistline and hypertension significantly mediated the association between CTI and diarrhea.

Conclusion: CTI is associated with the occurrence of diarrhea and may serve as a useful biomarker for identifying individuals at higher risk of diarrhea.

Supplementary Information: The online version contains supplementary material available at 10.1186/s12876-025-04158-6.