Glomerular filtration rate and kidney size after six years disease duration in non-insulin-dependent diabetic subjects.
The objective of the present study was to estimate how glomerular filtration rate and kidney size change after six years of diabetes in subjects with non-insulin-dependent disease. It is a population-based prospective study of a cohort of non-insulin diabetic patients (n = 150) diagnosed 1985-1988. The baseline studies utilized a non-diabetic control group, whose basic characteristics were equal to the study group. The setting was a primary health care center in an urban area. Main outcome measures were the glomerular filtration rate and its relation to renal area, mean blood pressure, hemoglobin A1c, serum insulin and cholesterol. Seventeen patients had died and 109 were eligible for evaluation at follow-up. The mean (standard deviation) of the glomerular filtration rate (ml/min/1.73 m2) remained elevated at follow-up, 118 (28), just as it was at baseline, 118 (28) in the diabetic subjects compared to matched non-diabetic subjects, 103 (24) (p = 0.0000). Kidney size (cm2) was larger in diabetic subjects at follow-up, 114 (19) than at baseline, 109 (18) (p = 0.0000) and in non-diabetic subjects 98 (14) (p < 0.0000). This resulted in a decline in glomerular filtration rate per unit renal area in the diabetic subjects at follow-up, 1.0 (0.23) compared to at baseline, 1.09 (0.23) (p = 0.002) and to non-diabetic subjects, 1.07 (0.23). The renal area at baseline was directly and significantly related to the glomerular filtration rate at follow-up (p < 0.001). The relation of baseline serum cholesterol, hemoglobin A 1c and mean arterial blood pressure to the glomerular filtration rate at follow-up was inverse and reached significance in those diabetic subjects having had high filtration rates at baseline but displaying a faster decline than on average i.e. in those patients who were at increased risk of renal insufficiency. We conclude that after the first six years of non-insulin-dependent diabetes the glomerular filtration rate remains high. Kidney size increases further from the attained increase at diagnosis and is an important determinant of continuing hyperfiltration. The deleterious effect of serum cholesterol and high blood glucose on the glomerular filtration rate at this early stage of diabetic kidney disease is suggestive.