NORMOALBUMINURIA ENSURES NO REDUCTION OF RENAL-FUNCTION IN TYPE-1 (INSULIN-DEPENDENT) DIABETIC-PATIENTS

Recent reports have suggested that impaired renal function in type 1 diabetic patients may be present despite normal urinary albumin excretion (UAE). We have studied kidney function by means of a constant-infusion technique in normoalbuminuric type 1 diabetic patients without antihypertensive medication (UAE < 20-mu-g min-1, n = 134), in microalbuminuric patients (20 greater-than-or-equal-to UAE < 200-mu-g min-1, n = 50) and in 27 non-diabetic control subjects. Mean UAE was 4.5-mu-g min-1 (range 1.0-19.3-mu-g min-1) in normoalbuminuric patients, 53.1-mu-g min-1 (range 20.8-147.5-mu-g min-1) in microalbuminuric patients, and 4.0-mu-g min-1 (range 2.1-17.9-mu-g min-1) in controls. Glycosylated haemoglobin A1c was significantly higher in microalbuminuric patients (8.9%, range 5.9-12.6%) than in normoalbuminuric patients (7.9%, range 5.5-11.5%) (P < 0.0001). Glomerular filtration rate in normoalbuminuric patients (135 ml min-1, range 97-198 ml min-1) was significantly higher than in controls (118 ml min-1, range 94-139 ml min-1) (P < 1 x 10(-6)), and significantly lower than in microalbuminuric patients (142 ml min-1, range 100-186 ml min-1) (P < 0.05). Mean arterial blood pressure was lower in normoalbuminuric patients (91 mmHg, range 78-108 mmHg) than in microalbuminuric patients (98 mmHg, range 82-131 mmHg) (P < 1 x 10(-6)), but not significantly different from that of controls (89 mmHg, range 73-103 mmHg). We conclude that normal UAE is a reliable indicator of well-preserved renal function. Glomerular hyperfiltration, elevated blood pressure and poor metabolic control are characteristic features of microalbuminuric patients.