High cardiovascular risk in patients with Type 2 diabetic nephropathy: the predictive role of albuminuria and glomerular filtration rate. The NID-2 Prospective Cohort Study.

Background: In Type 2 diabetic patients, clinical diagnosis of diabetic nephropathy (DN) is generally based on the concomitant presence of abnormal albuminuria and severe retinopathy. In this high-risk population, cardiovascular (CV) outcome has never been evaluated.

Methods: A cohort of 742 Type 2 diabetic patients with DN from 17 national centres was selected by the presence of persistent albuminuria ≥ 30 mg/day and severe diabetic retinopathy and was followed prospectively. Time to CV event (CV death, non-fatal myocardial infarction, non-fatal stroke, revascularization, major amputation) was the primary composite end point and it was analysed by multivariable Cox's proportional hazards model. The interaction between albuminuria and glomerular filtration rate (GFR) was specifically investigated.

Results: Median follow-up was 4.6 years. Overall 242 events (26% of which fatal) were observed in 202 patients. The proportion of CV events increased from 19 to 40% as GFR declined from the highest (≥ 90 mL/min/1.73 m(2)) to the lowest (<45 mL/min/1.73 m(2)) category and was equal to 25 and 33% in microalbuminuria and macroalbuminuria, respectively. In multivariable analysis, the interaction between albuminuria and GFR was statistically significant (P = 0.012). Albuminuria, indeed, had a remarkable prognostic effect in subjects with high GFR that virtually disappeared as GFR became <30 mL/min/1.73 m(2). Age, smoking habit, previous occurrence of myocardial infarction or stroke and proliferative retinopathy were all found to have a statistically significant prognostic effect on CV outcome.

Conclusions: A clinically based diagnosis of DN in Type 2 diabetes allows the identification of subjects with high CV risk. Albuminuria has a relevant prognostic effect on CV morbidity and mortality; its effect is especially pronounced when GFR is normal or near normal.