title: Inverse Association between Serum Bilirubin Levels and Retinopathy in Patients with Type 2 Diabetes Mellitus.
abstract: BACKGROUND
  Oxidative stress plays a central role in the pathogenesis of Diabetic Retinopathy (DR) and serum bilirubin has been shown to have antioxidant properties.
  
  
  OBJECTIVE
  To investigate the association between serum bilirubin concentration and DR in patients with Type 2 Diabetes Mellitus (DM).
  
  
  METHODS
  This was a hospital based, cross- sectional study where in 86 patients with Type 2 DM and 30 controls were recruited. The study was conducted at a tertiary care centre in Southern India between January 2014 and December 2014. The presence and the severity of DR were determined by fundus examination and grading of colour fundus photographs using the international clinical disease severity scale for DR. Serum total, direct and indirect bilirubin levels were determined in all subjects and the association between bilirubin levels and severity of DR was studied.
  
  
  RESULTS
  Among the 86 diabetics, 24 had no retinopathy and 62 had DR of varying grades. The mean total bilirubin level among diabetic subjects (0.52±0.17) and controls (0.51±0.19) were found to be similar. The mean total as well as direct bilirubin levels were found to be lower in patients with retinopathy as compared to no retinopathy group (p<0.001). The severity of DR was inversely proportional to the serum bilirubin levels (p=0.010). Serum total bilirubin was found to have a negative association with glycosylated haemoglobin and served as an independent determinant of DR even after adjusting for risk factors known to be associated with DR (p=0.001).
  
  
  CONCLUSIONS
  Low serum bilirubin levels are significantly associated with increased risk of DR independent of classic risk factors. Serum bilirubin can serve as a useful biomarker in identifying patients at risk for developing proliferative DR.
authors.affiliation: Associate Professor, Department of Ophthalmology, PSG Institute of Medical Sciences and Research , Coimbatore, Tamilnadu, India .
authors.forename: Divya
authors.initials: D
authors.lastname: Karuppannasamy
authors.affiliation: Medical Officer, Department of Ophthalmology, Aravind Eye Hospitals , Theni, Tamilnadu, India .
authors.forename: Raghuram
authors.initials: R
authors.lastname: Venkatesan
authors.affiliation: Assistant Professor, Department of Ophthalmology, PSG Institute of Medical Sciences and Research , Coimbatore, Tamilnadu, India .
authors.forename: Lekha
authors.initials: L
authors.lastname: Thankappan
authors.affiliation: Consultant Vitreoretinal Surgeon, Department of Ophthalmology, PSG Institute of Medical Sciences and Research , Coimbatore, Tamilnadu, India .
authors.forename: Raghuram
authors.initials: R
authors.lastname: Andavar
authors.affiliation: Professor, Department of Ophthalmology, PSG Institute of Medical Sciences and Research , Coimbatore, Tamilnadu, India .
authors.forename: Sundar
authors.initials: S
authors.lastname: Devisundaram
keywords: Chronic kidney disease; Heme oxygenase; Peripheral arterial disease