THE PREDICTIVE VALUE OF MICROALBUMINURIA IN IDDM - A 5-YEAR FOLLOW-UP-STUDY

OBJECTIVE - To investigate the predictive value of microalbuminuria an d the annual increase of albumin excretion as risk factors for diabeti c nephropathy. RESEARCH DESIGN AND METHODS - A 5-year follow-up of pat ients 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 collec tion. The annual increase in UAE was calculated by linear regression a nalysis of log-transformed UAE on time. This study was conducted at th e outpatient clinic of the Steno Diabetes Center. The study subjects i ncluded 118 insulin-dependent diabetes mellitus (IDDM) patients betwee n 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 (percent age per year), and the prevalence of retinopathy. RESULTS - After 5 ye ars, 39 (33%, 24-42 CI (95% confidence interval]) patients with microa lbuminuria had normoalbuminuria, 57 (48%, 38-57 CI) still had microalb uminuria, and 22 (19%, 12-27 CI) had developed diabetic nephropathy. A mong the 112 patients with normoalbuminuria in 1985, 9 (8%, 4-15 CI) h ad developed microalbuminuria, and 2 (2%, 0-6 CI) had developed diabet ic nephropathy. Of the 79 patients with persistent albuminuria, only 3 6 (46%, 34-57 CD were progressors with a rate of progression of >5%/ye ar. Progressors had significantly higher HbA1c, higher mean blood pres sure, and a higher incidence of proliferative retinopathy compared wit h nonprogressors. Multiple regression analysis only identified mean Hb A1c as an independent predictor of the rate of progression. Smoking wa s significantly more prevalent in patients with persistent albuminuria . CONCLUSIONS - Microalbuminuria is a predictor of progression to diab etic nephropathy; however, not as strong as suggested previously. Calc ulation of the annual increase in UAE seems to be a more specific meth od of identifying patients who will develop diabetic nephropathy.