Impact of metabolic control in progression of clinical diabetic nephropathy

Renal clearance of 51Cr-EDTA as a measure of glomerular filtration rate was followed prospectively for 21 months in 18 Type 1 (insulin-dependent) patients with juvenile-onset diabetes and nephropathy. Hypertension was treated aggressively, attaining a mean blood pressure of 154/88 mmHg in the supine and 126/82 mmHg in the standing position. The mean glycosylated haemoglobin value (HbA1c) during the observation period was found to correlate well with the mean of random blood glucose values (r = 0.72). It also correlated to the rate of glomerular filtration rate decline over time, whether the latter was calculated as slope coefficient for all available data (r = -0.52, p less than 0.05) or based on the first and last observations only (r = -0.57, p less than 0.05). In a multiple linear stepwise regression analysis also including mean arterial blood pressure, the correlation between glomerular filtration rate decline and HbA1c was significant at p less than 0.01; this explained one-third of the progression, while mean arterial pressure could not be shown to contribute. It is concluded that hyperglycaemia, contrary to the general belief, is a risk factor for the progression of clinical diabetic nephropathy with reduced glomerular filtration rate.