To investigate the predictive value of microalbuminuria and the annual increase of albumin excretion as risk factors for diabetic nephropathy.
A 5-year follow-up of patients with microalbuminuria (urinary albumin excretion [UAE\ = 30-299 mg/24 h) and matched patients with normoalbuminuria (UAE < 30 mg/24 h). The initial classification was based on one single 24-h urine collection. The annual increase in UAE was calculated by linear regression analysis of log-transformed UAE on time. This study was conducted at the outpatient clinic of the Steno Diabetes Center. The study subjects included 118 insulin-dependent diabetes mellitus (IDDM) patients between 18 and 50 years of age with microalbuminuria and 112 matched control patients with normal UAE with an age at diabetes onset of <31 years. The main outcome measures were UAE, annual change in UAE rate (percentage per year), and the prevalence of retinopathy.
After 5 years, 39 (33%, 24-42 CI [95% confidence interval]) patients with microalbuminuria had normoalbuminuria, 57 (48%, 38-57 CI) still had microalbuminuria, and 22 (19%, 12-27 CI) had developed diabetic nephropathy. Among the 112 patients with normoalbuminuria in 1985, 9 (8%, 4-15 CI) had developed microalbuminuria, and 2 (2%, 0-6 CI) had developed diabetic nephropathy. Of the 79 patients with persistent albuminuria, only 36 (46%, 34-57 CI) were progressors with a rate of progression of >5%/year. Progressors had significantly higher HbA1c, higher mean blood pressure, and a higher incidence of proliferative retinopathy compared with nonprogressors. Multiple regression analysis only identified mean HbA1c as an independent predictor of the rate of progression. Smoking was significantly more prevalent in patients with persistent albuminuria.
Microalbuminuria is a predictor of progression to diabetic nephropathy; however, not as strong as suggested previously. Calculation of the annual increase in UAE seems to be a more specific method of identifying patients who will develop diabetic nephropathy.