Proliferative retinopathy predicts nephropathy: a 25-year follow-up study of type 1 diabetic patients

We wanted to examine proliferative retinopathy as a marker of incident nephropathy in a 25-year follow-up study of a population-based cohort of Danish type 1 diabetic patients and to examine cross-sectional associations between nephropathy and retinopathy in long-term surviving patients of the same cohort. All type 1 diabetic patients from Fyn County, Denmark, were identified as of 1 July 1973. One hundred and eighty four patients were examined in 1981–1982 (baseline) and in 2007–2008 (follow-up). The level of retinopathy was graded by ophthalmoscopy at baseline and nine-field digital colour fundus photographs at follow-up. Single spot urine was used to evaluate nephropathy at both examinations. Proliferative retinopathy was present in 29 patients (15.8%) at baseline. At follow-up, these patients were more likely to macroalbuminuria (20.7% vs. 6.5%) than patients without proliferative retinopathy at baseline. In a multivariate logistic regression adjusted for baseline age, sex, duration of diabetes, smoking, HbA_1, systolic and diastolic blood pressure, odds ratio of nephropathy (micro- and macroalbuminuria combined) was 2.98 (95% confidence interval 1.18–7.51, p = 0.02) for patients with proliferative retinopathy at baseline as compared to those without. At follow-up, there was a close relation between retinopathy and nephropathy. The level of macroalbuminuria was 4.3, 4.6 and 13.0% for patients with no or mild non-proliferative retinopathy, moderate non-proliferative retinopathy and proliferative retinopathy, respectively. In conclusion, proliferative retinopathy is an independent marker of long-term nephropathy in type 1 diabetes. Upcoming studies should examine whether these microvascular complications are also causally linked in type 1 diabetes.