Bilirubin concentration is positively associated with haemoglobin concentration and inversely associated with albumin to creatinine ratio among Indigenous Australians: eGFR Study

Low serum bilirubin concentrations are reported to be strongly associated with cardio-metabolic disease, but this relationship has not been reported among Indigenous Australian people who are known to be at high risk for diabetes and chronic kidney disease (CKD). Hypothesis: serum bilirubin will be negatively associated with markers of chronic disease, including CKD and anaemia among Indigenous Australians. Method: A cross-sectional analysis of 594 adult Aboriginal and Torres Strait Islander (TSI) people in good health or with diabetes and markers of CKD. Measures included urine albumin: creatinine ratio (ACR), estimated glomerular filtration rate (eGFR), haemoglobin (Hb) and glycated haemoglobin (HbA1c). Diabetes was defined by medical history, medications or HbA1c ≥ 6.5% or ≥ 48 mmol/mol. Anaemia was defined as Hb < 130 g/L or < 120 g/L in males and females respectively. A multivariate regression analysis examining factors independently associated with log-bilirubin was performed. Results: Participants mean (SD) age was 45.1 (14.5) years, and included 62.5% females, 71.7% Aboriginal, 41.1% with diabetes, 16.7% with anaemia, 41% with ACR > 3 mg/mmol and 18.2% with eGFR < 60 mL/min/1.73m². Median bilirubin concentration was lower in females than males (6 v 8 μmol/L, p < 0.001) and in Aboriginal than TSI participants (6 v 9.5 μmol/L, p < 0.001). Six factors explained 35% of the variance of log-bilirubin; Hb and cholesterol (both positively related) and ACR, triglycerides, Aboriginal ethnicity and female gender (all inversely related). Conclusion: Serum bilirubin concentrations were positively associated with Hb and total cholesterol, and inversely associated with ACR. Further research to determine reasons explaining lower bilirubin concentrations among Aboriginal compared with TSI participants are needed.