# Association of Serum Total Bilirubin Level With Abdominal Aortic Calcification: A Population-Based Cross-Sectional Study

## TL;DR

This study finds that higher or lower bilirubin levels are linked to increased abdominal aortic calcification in a U-shaped pattern, suggesting optimal bilirubin levels may help prevent this condition.

## Contribution

The study is the first to demonstrate a U-shaped association between serum bilirubin and abdominal aortic calcification in a U.S. population.

## Key findings

- Serum total bilirubin levels show a U-shaped association with abdominal aortic calcification prevalence.
- Higher odds of calcification are observed in the highest and lowest bilirubin quartiles after adjusting for confounders.
- The U-shaped relationship is strongest in older adults, those with hypertension, diabetes, or obesity.

## Abstract

Objective: The purpose of our study was to examine the association between serum total bilirubin level and abdominal aortic calcification (AAC) in the general United States population.

Methods: We analyzed data from the 2013–2014 National Health and Nutrition Examination Survey (NHANES) to assess the association of total bilirubin levels with AAC and severe AAC (SAAC). Restricted cubic spline (RCS) plots, weighted multivariable logistic regression (odds ratios [ORs] and 95% confidence intervals [CIs]), and stratified subgroup analyses (by age, sex, hypertension, diabetes mellitus, and body mass index [BMI]) were conducted.

Results: Our analysis included a total of 3016 participants. First, the RCS plots showed the U-shaped curve association of serum total bilirubin level with prevalence of AAC and SAAC. RCS analysis revealed a U-shaped association between serum total bilirubin levels and the prevalence of both AAC and SAAC. Serum total bilirubin levels were categorized into quartiles: Q1 (0.10–0.50 mg/dL), Q2 (0.51–0.60 mg/dL), Q3 (0.61–0.80 mg/dL), and Q4 (0.81–2.20 mg/dL). Second, after adjusting for potential confounders, compared with the Q1 group, the ORs with 95% CI for the association of total bilirubin level with AAC and SAAC across Q2, Q3, and Q4 were (0.71 (0.61, 0.98), 1.11 (0.90, 1.38), and 1.36 (1.07, 1.73) and 0.78 (0.58, 1.21), 1.12 (0.77, 1.65), and 1.28 (0.87, 1.77)), respectively. Finally, this U-shaped correlation was found among participants in age ≥60 years, with hypertension, with DM and with BMI of ≥30 kg/m2.

Conclusions: Our study identified a significant U-shaped association between serum total bilirubin levels and both AAC and SAAC. These findings suggested that monitoring and optimizing total bilirubin levels may offer potential preventive benefits against AAC development.