Objective: To investigate the predictive value of microalbuminuria (albumin excretion rate 30-300 mg/24 h) as a risk factor for overt diabetic nephropathy in patients with longstanding insulin dependent diabetes.
Design: 10 year follow up of patients with normoalbuminuria (albumin excretion rate < 30 mg/24 h), microalbuminuria (30-300 mg/24 h), and macroalbuminuria (> 300 mg/24 h) based on two out of three timed overnight urine samples.
Setting: Outpatient clinic of Helsinki University Hospital.
Subjects: 72 consecutive patients who had had insulin dependent diabetes for over 15 years.
Main outcome measures: Urinary albumin excretion rate, mortality, and prevalence of diabetic complications after 10 years.
Results: 56 patients were re-examined at 10 year follow up, 10 had died, five were lost to follow up, and one was excluded because of non-diabetic kidney disease. At initial screening 22 patients had macroalbuminuria, 18 had microalbuminuria, and 26 had normal albumin excretion. Only five (28%, 95% confidence interval 10% to 54%) of the microalbuminuric patients developed macroalbuminuria during the 10 year follow up and none developed end stage renal failure. Two (8%, 1% to 25%) normoalbuminuric patients developed macroalbuminuria and four (15%, 4% to 35%) became microalbuminuric. Seven (32%, 14% to 55%) of the macroalbuminuric patients developed end stage renal failure and six (27%, 11% to 50%) died of cardiovascular complications.
Conclusion: Microalbuminuria is not a good predictor of progression to overt nephropathy in patients with longstanding insulin dependent diabetes.