A Cross-sectional study to analyze the association between serum bilirubin and chronic kidney disease from Jinchang Cohort China

Objective: To analyze the association between serum bilirubin levels (total, direct, and indirect) and Chronic Kidney Disease (CKD) in the Jinchang cohort. The study aimed to further investigate the impact of serum bilirubin levels on the incidence rate of CKD, and to provide new perspectives for the early identification of high-risk populations and the prevention and treatment of CKD. Methods: A cross-sectional analysis was conducted on a cohort of 43,161 individuals from Jinchang who completed their baseline survey between June 2011 and December 2013. Participants were categorized into quartiles based on their serum bilirubin levels. The prevalence increases with age and rises significantly, especially among people over 70 years of age. An unconditional logistic regression model was employed to evaluate the impact of serum bilirubin levels on CKD. Additionally, a Regression Discontinuity Design (RDD) was utilized to examine potential threshold effects between serum bilirubin levels and CKD. Results: Among 43,161 participants, 1,907 (4.42%) were diagnosed with CKD. The prevalence was higher in males than in females (4.86% vs. 3.74%). CKD prevalence increased with age across all gender groups. CKD prevalence increased with age across all gender groups, with a significant increase in those over 60 years of age. After adjusting for confounders, compared with Q1 concentration group, the risk of CKD in serum total bilirubin Q2-Q4 concentration group was reduced by 13.7% (OR: 0.863, 95%CI: 0.756-0.986) and 14.9% (OR: 0.851, 95%CI: 0.744-0.972) and 18.9% (OR: 0.811, 95%CI: 0.709-0.928); The risk of CKD in serum indirect bilirubin Q2-Q4 concentration group was reduced by 14.8% (OR: 0.852, 95%CI: 0.750-0.968), 27.6% (OR: 0.724, 95%CI: 0.634-0.827) and 27.8% (OR: 0.722, 95%CI: 0.632-0.825); the risk of CKD in serum direct bilirubin Q4 concentration group was increased by 28.0% (OR: 1.280, 95%CI: 1.123-1.459) in those with serum direct bilirubin Q4 concentrations. RDD analysis between serum bilirubin levels and CKD found that the risk of CKD in the general population "jumps" up by 0.7% (P=0.003) only when serum direct bilirubin =4.0μmol/L. Conclusions : The Jinchang cohort displayed a relatively low prevalence of CKD. High levels of total and indirect bilirubin were associated with a reduced risk of CKD, suggesting a protective effect. In contrast, elevated direct bilirubin levels were identified as a risk factor for CKD. A notable threshold effect was observed at a serum direct bilirubin level of 4.0 μmol/L, beyond which the risk of CKD increased.