With the aim of defining the transitional phase from normal or near normal albumin excretion to overt diabetic nephropathy, 23 male diabetics of more than 7 years' duration, below 40 years of age and a baseline urinary albumin excretion above 15 μg/ min but without clinical proteinuria (incipient diabetic nephropathy) were studied. For comparison 18 normals, 23 diabetics with normal albumin excretion and 10 patients with overt nephropathy were also examined. Diastolic blood pressure (DBP) was elevated to 88±9mmHg (mean±S.D.) compared to patients with normal urinary albumin excretion: 80±7 (S.D.) (2 p =0.13%) but was below pressures in patients with overt diabetic nephropathy 109±15 (2 p = 0.002%). Glomerular filtration rate (GFR) was elevated to 142±21 ml/min (mean±S.D.) compared to 132±9 in patients with normal urinary albumin excretion (2 p =4.3%). Renal plasma flow (RPF) was not altered. Renal vascular resistance (RVR) was increased (0.200±0.035) compared to that of patients with normal urinary albumin excretion (0.180±0.025) (2 p = 3.8%). In a longitudinal study of 10 of the patients with incipient nephropathy, followed for 4.9 (Mean) years, urinary albumin excretion increased significantly during the observation period, the yearly increase rate being 19±22% (mean±S.D.). DBP increased from 84±9 to 93±13 (2 p = 3.8%) in 6 patients followed for more than 4 years. A significant correlation was observed between DBP and the yearly percentage increase rate in urinary albumin excretion ( r = 0.77, 2 p = 0.9%) and between RVR and the yearly percentage increase rate in urinary albumin excretion ( r = 0.80, 2 p = 0.8%). Thus incipient diabetic nephropathy is associated with high GFR and with elevated blood pressure both of which may accelerate further renal damage.
Christensen et al. (1985) studied this question.