• blood pressure;
  • glomerular filtration rate;
  • type 1 diabetes;
  • urinary albumin excretion

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 μg min−1, n = 134), in microalbuminuric patients (20 ≥ UAE < 200 μg min−1, n = 50) and in 27 non-diabetic control subjects. Mean UAE was 4.5 μg min−1 (range 1.0–19.3 μg min−1) in normoalbuminuric patients, 53.1 μg min−1 (range 20.8–147.5 μg min−1) in microalbuminuric patients, and 4.0 μg min−1 (range 2.1–17.9 μg 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 times 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 times 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.