Near-normal urinary albumin concentrations predict progression to diabetic nephropathy in Type 1 diabetes mellitus

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Abstract
SUMMARY Aims To determine urinary albumin concentrations that predict progression to diabetic nephropathy and sight-threatening diabetic retinopathy and identify baseline parameters associated with progression. Methods One thousand two hundred and one Type 1 diabetic patients aged 35 years or younger at diagnosis attending six hospital diabetes clinics in Scotland and included on the Royal College of Physicians of Edinburgh Diabetes Register were followed for a median (interquartile range) of 4.0 (2.5–5.5) years. Diabetic nephropathy was defined as the geometric mean of two consecutive urinary albumin values > 200 mg/l or a single value > 1000 mg/l. Retinopathy was defined as clinician-determined maculopathy or proliferative retinopathy. Results Forty-six patients developed nephropathy (4%) and 98 retinopathy (8%). Cox proportional hazards analyses demonstrated that a baseline urinary albumin concentration above 7.4 mg/l, longer duration of diabetes and higher HbA1c levels predicted the development of nephropathy. Higher baseline urinary albumin concentrations were the most powerful predictor for the development of nephropathy. Longer duration of diabetes, baseline blood pressure > 140/90 mmHg and higher HbA1c levels all predicted the development of sight-threatening retinopathy whereas baseline urinary albumin concentration did not. Conclusions Elevation of urinary albumin concentration just above the normal range is associated with an increased risk of developing diabetic nephropathy. Identifying patients with any abnormalities of urinary albumin excretion will provide a clear rationale for early therapeutic interventions.