Background and aims: Hyperglycaemia is a strong risk factor for the development of renal disease in insulin dependent diabetes mellitus but it is uncertain whether it contributes to the progression of incipient or established nephropathy. The rigorous treatment of blood pressure in recent years may help uncover the contribution of hyperglycaemia, if any, to the progression of renal failure. Our aim therefore, was to assess in a current cohort of insulin dependent diabetic patients with diabetic nephropathy the relative importance of glycaemic control and blood pressure on disease progression.
Methods: All insulin dependent diabetic patients with persistent albuminuria (> 300 mg/24 h) attending the diabetic clinic at Guy's Hospital between 1977 and 1993 were recruited. Serial measurements of blood pressure, HbA1 and GFR were performed every 6 months until end-stage renal disease or death. Only patients with at least 1 year of follow up were analysed. The mean follow up period was 8 years (range 1.5-15.5 years). Baseline and time dependent variables were related to the rate of change of GFR using weighted linear regression and stepwise multiple regression analysis. The impact of each variable on the change of GFR with time was adjusted for the effect of other potentially confounding variables by analysis of co-variance.
Results: Patients had well-controlled blood pressure throughout the observation period (mean arterial pressure 97 +/- 8 mmHg) and the average rate of decline of GFR was 4.32 +/- 4.08 ml/min/year. In univariate analysis baseline and mean HbA1 were linearly related to the rate of decline of GFR (baseline r5-0.565, P < 0.001; mean r-0.5107, P < 0.001) with those with a higher HbA1 having a faster rate of progression. In stepwise multivariate analysis both mean HbA1 mean diastolic blood pressure (P < 0.0001 and P = 0.019, respectively) was significantly and independently related with a faster rate of decline of GFR.
Conclusions: Worse glycaemic control is associated with a faster rate of progression of diabetic nephropathy once blood pressure is controlled. Thus improvement of glycaemic control in patients where good blood pressure control has been achieved may potentially further delay the progression of nephropathy.