Serum direct bilirubin and indirect bilirubin levels were both associated with diabetic nephropathy

Objective To assess the correlation between serum bilirubin levels (including direct bilirubin and indirect bilirubin) and estimated glomerular filtration rate (eGFR), urinary albumin excretion in type 2 diabetic mellitus patients. Methods A total of 2 390 patients with type 2 diabetes were included. Serum total bilirubin, direct bilirubin, indirect bilirubin, eGFR, urine albumin/uric creatinine rate (UACR) and other information were collected retrospectively. Patients were divided into 4 groups based on the total bilirubin, direct bilirubin and indirect bilirubin separately (from low to high T1 to T4 group, D1 to D4 group and I1 to I4 group). Results UACR was significantly higher in T1 group than that in T2, T3 and T4 groups: 18.79 (10.67, 53.99) mg/g vs. 15.91 (9.86, 36.12), 16.10 (9.35, 29.75) and 16.38 (9.95, 33.44) mg/g (P < 0.01); and eGFR was significantly lower. In D1 to D4 group and I1 to I4 groups, there were statistical differences in UACR and eGFR (P<0.01). Pearson correlation analyses showed that serum total bilirubin, direct bilirubin and indirect bilirubin were positively correlated with eGFR (r= 0.107, 0.076 and 0.110; P < 0.01), and inversely correlated with UACR (r=-0.093,-0.078 and-0.090; P < 0.01). Multiple linear regression analysis showed linear relationships between serum total bilirubin, direct bilirubin, indirect bilirubin and eGFR, UACR still existed after adjustment of age, gender, duration of diabetes, BMI, glycosylated hemoglobin A1c and diastolic blood pressure (P < 0.05). Conclusions Serum total bilirubin, direct bilirubin and indirect bilirubin are all positively correlated with eGFR, and inversely correlated with UACR. Key words: Bilirubin; Diabetic nephropathy; Glomerular filtration rate; Albumin excretion