Urinary albumin excretion rate and glomerular filtration rate in the prediction of diabetic nephropathy; a long-term follow-up study of childhood onset type-1 diabetic patients.

BACKGROUND: Predictors of diabetic nephropathy are only partly known. The role of glomerular hyperfiltration is much discussed. We have studied the cumulative incidence of micro and macroalbuminuria and the predictive value of glomerular filtration rate (GFR) and screening value of albumin excretion rate (AER) in type-1 diabetes.
METHODS: A cohort of diabetic children was followed up at a mean duration of 29+/-3 years. All 75 children treated in one hospital with diabetes duration > or =8 years were prospectively followed for 8 years examining GFR, AER, blood pressure and HbA1c. After another 8-10 years, 60 of them were traced for endpoint follow-up.
RESULTS: Seven patients (12%) developed macroalbuminuria, i.e. persistent overnight AER>200 mg/min, 12 (20%) developed persistent microalbuminuria (AER 15-200 mg/min) and 17 (28%) transient microalbuminuria (>15 mg/min on two consecutive occasions, normalized at endpoint). One baseline screening value of 24-h AER>15 mg/min predicted 93% of patients with persistent micro or macroalbuminuria. The negative predictive value was 78%. Six of seven macroalbuminuric and 10 of 12 microalbuminuric patients had a baseline GFR above the normal limit of the method (> or =125 ml/min/1.73 m(2)). When adjusted for diabetes duration, increased GFR predicted macro or microalbuminuria (odds ratios=5.44, P=0.04). The positive predictive value for having an increased baseline GFR was 53%. The negative predictive value was 77%. Stratification for HbA1c did not change the effect of an increased GFR.
CONCLUSIONS: At a mean diabetes duration of 29 years the cumulative incidence of macroalbuminuria was 12%; however, another 20% had persistent microalbuminuria. A screening value of 24-h AER >15 mg/min was a strong predictor, whereas increased GFR was a weaker but significant predictor for micro and macroalbuminuria.