Association between serum bilirubin and estimated glomerular filtration rate among elderly persons

Chronic kidney disease (CKD) is a major public health problem. However, few studies have examined the significance of serum bilirubin as a risk factor for the development of CKD in the general Japanese population. The subjects comprised 413 men (mean age: 79±9 years; (range, 60-100 years) and 637 women (mean age: 81±8 years; range, 60-106 years) who visited the medical department of Seiyo Municipal Nomura Hospital. We examined the relationship between increased serum bilirubin and renal function that was evaluated by estimated glomerular filtration rate (eGFR) using CKD-EPI equations modified by a Japanese coefficient. Stepwise multiple regression analysis with eGFR as the objective variable, and adjusted risk factors as the explanatory variables, showed that serum bilirubin (β = 0.11, P<0.001) was significantly and independently associated with eGFR, in addition to gender, age, prevalence of antihypertensive medication, triglycerides, prevalence of antidiabetic medication, and serum uric acid. Compared with stages 1+2 (eGFR ≥60.0 ml/min/1.73 m2), mean multivariate-adjusted odds ratio {95% (confidence interval (CI)} for hypobilirubinemia (first quartile, <0.52 mg/dL) was 3.52 (range: 1.88-6.59). Next, to control potential confounding factors, data were further stratified by gender, age, medication (antihypertensive, antidyslipidemic, and antidiabetic agents), and prevalence of cardiovascular disease. The standardized coefficient for eGFR was significant in both groups, and there was no interaction between the groups. Our data demonstrated an independent positive association between serum bilirubin and eGFR in both genders. Low serum bilirubin level would be useful as a potential risk factor for renal function.