Objective: To examine the validity of the time honored threshold value for microalbuminuria of 30 mg/24 h, by analyzing an 8-year follow-up data of 599 patients with diabetes mellitus type 2, normal blood pressure and base-line albumin excretion rate (AER) </=30 mg/24 h.
Patients: The patients were allocated to three groups according to the baseline values of AER. Group I: 0-10 mg/24 h; Group II: 10.1-20 mg/24 h; Group III: 20.1-30 mg/24 h.
Results: Progression to microalbuminuria during follow-up occurred in 25.3, 47.3 and 85.3% of the patients in Group I, II and III, respectively. Compared to Group I, the risk to progress to microalbuminuria was 2. 34 (95% CI 1.32-4.43, P=0.029) in patients of Group II and 12.36 (95% CI 8.9-16.5, P=0.0001) in Group III. The average annual decline in glomerular filtration rate (GFR) was 1.19, 1.64 and 2.52 ml/min per year, respectively in the three groups. The correlation between baseline AER values and subsequent decline in GFR was exponential without a clear threshold value. Compared to Group I, the odds ratio for any cardiovascular end point (e.g. death, non-fatal myocardial infarction etc.) was 1.9 (95% CI 0.8-2.5, P=0.22) for patients of Group II and 9.8 (95% CI 6.7-12.3, P=0.001) for Group III.
Conclusions: The present study shows that patients with baseline AER values of 20.1-30 mg/24 h show an accelerated decline in GFR and significantly higher risk for cardiovascular events than patients with AER values below 20 mg/24 h. Though AER is obviously a continuous variable, the arbitrary threshold value for screening and for preventive strategies should probably be set at 20 rather than at 30 mg/24 h.