Relationship between serum indirect bilirubin and prostate volume in patients with benign prostatic hyperplasia: a cross-sectional study.

Background: Due to its anti-oxidative effects, bilirubin may protect against a spectrum of diseases. However, the role of bilirubin in patients with benign prostatic hyperplasia (BPH) is poorly explored. This study aimed to investigate the cross-sectional associations between serum indirect bilirubin (IBIL) and prostate volume (PV) in patients with BPH.

Methods: The medical records of 722 BPH patients were retrospectively analyzed. Body mass index (BMI) was calculated as body weight (kg)/height (m). PV was obtained as height (cm) × width (cm) × length (cm) × π/6. Other biochemical indexes were measured by the automatic biochemical analyzer. A univariable linear regression analysis was performed to detect confounders. The IBIL-PV relationship was examined using unadjusted and covariate-adjusted regression models. Furthermore, a segmented linear regression was conducted to analyze the linear trend of IBIL levels and PV. Finally, the sensitivity analysis was stratified by BMI and low-density lipoprotein cholesterol (LDL-C) cutoffs.

Results: In this study, the mean age of the patients was 68 (range, 43-93) years. By univariable line regression test, we observed that PV was positively correlated with age, BMI, and LDL-C (β=0.113, 0.096, and 0.135, respectively). IBIL was negatively associated with PV in full adjusted model in men age ≤75 years (β=-1.01; 95% CI: -1.81, -0.22; P=0.01). A statistically significant inverse trend was observed between serum IBIL intervals and PV in patients aged ≤75 years (adjusted for age, BMI, and LDL-C, P for trend =0.015). In sensitivity analysis, significantly negative IBIL-PV relationship only existed in men with normal BMI (adjusted β=-1.328; 95% CI: -2.467, -0.190; P=0.022), overweight men (adjusted β=-1.296; 95% CI: -2.519, -0.074; P=0.038), and men with normal LDL-C level (adjusted β=-1.017; 95% CI: -1.869, -0.164; P=0.019).

Conclusions: IBIL is negatively associated with PV in the non-obese population ≤75 years with normal LDL-C. These results suggest that higher serum IBIL possibly provides a degree of protection to BPH by mitigating oxidative stress (OS) related to aging and lipid peroxidation. Nevertheless, these preliminary findings from a single-center, retrospective study have limitations and need to be confirmed by future studies.