Low serum total bilirubin concentration in patients with type 1 diabetes mellitus complicated by retinopathy and nephropathy

Aims: Although a relationship between serum bilirubin concentration and diabetic microangiopathy in patients with type 2 diabetes has been reported, whether such a relationship exists in patients with type 1 diabetes is unknown. This study assessed the relationships between serum total bilirubin concentration and retinopathy/nephropathy in patients with type 1 diabetes. Methods: A total of 126 patients with type 1 diabetes were investigated in this cross-sectional study. Serum total bilirubin concentration was compared between patients with and without diabetic retinopathy/nephropathy, and among the categories stratified according to the severity of retinopathy/nephropathy. A logistic regression model was used to assess the association of retinopathy/nephropathy with total bilirubin. Finally, total bilirubin concentration was compared among patients with none, either, or both diabetic retinopathy and nephropathy. Results: Serum total bilirubin concentration was significantly lower in patients with retinopathy/nephropathy than in those without complications. Receiver operating characteristic analysis indicated that a bilirubin concentration of 0.55 mg/dl might be the appropriate threshold for the detection of retinopathy/nephropathy. Total bilirubin concentration differed significantly according to the severity of microangiopathy. In logistic regression analyses, total bilirubin level was significantly inversely associated with retinopathy/nephropathy. Moreover, bilirubin level in patients with either retinopathy or nephropathy was significantly higher than that in patients with both of them, and significantly lower than that in patients with neither of them. Conclusions: Total bilirubin concentration was shown to be lower in patients with type 1 diabetes complicated by retinopathy/nephropathy. Bilirubin might function protectively against microangiopathy in patients with type 1 diabetes.