The effect of metabolic control on rate of decline in renal function in insulin-dependent diabetes mellitus with overt diabetic nephropathy.

BACKGROUND Strict glycaemic control has been shown to reduce the risk of developing diabetic nephropathy. In established nephropathy, however, the impact of glycaemic control on prognosis is less clear. Therefore we investigated the effect of long-term glycaemic control on the decline in renal function in insulin-dependent diabetic patients with overt nephropathy. METHODS The study was performed at two hospital-based diabetes centres in western Sweden. The study was an observational retrospective follow-up study in 158 insulin-dependent diabetics with proteinuria with a mean (+/-SD) age of 36+/-9 years and a diabetes duration of 22+/-8 years. The change in glomerular filtration rate was measured as 51Cr EDTA clearance for a median of 8 years (range 1-17). Glycaemic control was determined with measurements of glycated haemoglobin A1c. RESULTS The decline in glomerular filtration rate was 3.8+/-3.7 ml/min/year. The blood pressure was 143/82+/-15/7 mmHg and the mean glycated haemoglobin was 8.7+/-1.6%. The correlation coefficient between glycated haemoglobin and decline in glomerular filtration rate was -0.39 (P<0.0001 ) and between decline in glomerular filtration rate and systolic and diastolic blood pressure -0.17 (P=0.03) and -0.29 (P=0.003) respectively. In patients with glycated haemoglobin <8.0% and diastolic blood pressure <85 mmHg the decline in glomerular filtration rate was 1.7+/-2.3 ml/min/year. CONCLUSIONS In this retrospective observational study, effective blood-pressure control was associated with a low rate of decline in renal function and a low urinary albumin excretion. The correlation between glycaemic control and decline in renal function indicates that poor glycaemic control can accelerate the loss of renal function in diabetic nephropathy.