The early natural history of nephropathy in type 1 diabetes: III. Predictors of 5-year urinary albumin excretion rate patterns in initially normoalbuminuric patients

Predictors of albumin excretion rate (AER) abnormalities could provide earlier indicators of diabetic nephropathy risk. Data from the Natural History Study, a prospective 5-year observation of renal structure and function in young type 1 diabetic patients, were examined for predictors of AER patterns in normoalbuminuric type 1 diabetic patients. Included were 170 patients (96 females) (aged 16.7 ± 5.9 years, duration of diabetes 8.0 ± 4.3 years) with normal blood pressure, normoalbuminuria (AER <20 μg/min), and eight or more follow-up visits over 5 years. AER, blood pressure, and HbA _1c (A1C) were determined quarterly and glomerular filtration rate (GFR) annually. Persistent microalbuminuria (PMA) was defined as 20-200 μg/min in two of three consecutive values within 6-12 months. Four different AER patterns were identified. Group 1 (n = 99): all values <20 μg/min. Group 2 (n = 49): intermittent levels >20 μg/min but not meeting microalbuminuria criteria. Group 3 (n = 14): PMA during follow-up but normoalbuminuria at study exit. Group 4 (n = 8): microalbuminuria at study exit. Group 4 (497 ± 95 nm, P < 0.01) and group 3 (464 ± 113 nm, P = 0.03) patients had greater baseline glomerular basement membrane (GBM) width versus group 1 (418 ± 67 nm). Baseline GFR in group 4 (163 ± 37 ml · min^-1 · 1.73 m^-2) was higher than group 1 (143 ± 28 ml · min^-1 · 1.73 m^-2, P = 0.04). A1C was higher in group 2 (9.0 ± 1.2%) than group 1 (8.4 ± 1.1%, P = 0.008). Thus, greater increases in GBM width and GFR were predictors of PMA. Since 64% of the patients that developed microalbuminuria reverted to normoalbuminuria, the risk of diabetic nephropathy as defined by current microalbuminuria criteria is unclear.