Exercise Testing as a Long-Term Predictor of the Development of Microalbuminuria in Normoalbuminuric IDDM Patients

OBJECTIVE To determine the association between exercise-induced albuminuria and the development of microalbuminuria over 10 years in subjects with insulin-dependent diabetes mellitus (IDDM) who were initially normoalbuminuric.

RESEARCH DESIGN AND METHODS Thirty-two patients with IDDM and a resting urinary albumin/creatinine ratio (U_A/U_C) <2.1 mg/mmol (< 15 μg/min) were exercised after water loading on a treadmill for 20 min at double their resting heart rate. U_A/U_C was determined before and after exercise. The exercise test was considered positive if the U_A/U_C was >4.3 mg/mmol (>30 μg/min). Results were compared with resting U_A/U_C after a 10-year follow-up. Persistent microalbuminuria was defined as a U_A/U_C >2.1 mg/mmol (> 15 μg/min) in each of two early-morning urine collections.

RESULTS Five patients developed persistent microalbuminuria after 10 years, and four patients were predicted by a positive exercise test. Two patients with positive exercise tests did not develop persistent microalbuminuria. The sensitivity of the exercise test for the development of microalbuminuria was 80% (95% confidence interval [CI] 65.8–94.2%) and the specificity was 92.9% (95% CI 83.9–100%). The postexercise U_A/U_C was positively associated with the U_A/U_C after 10 years (P = 0.005, R² = 0.31). This association was independent of HbA₁, systolic blood pressure, body mass index, and duration of diabetes, but HbA₁ remained an independent predictor (P = 0.02) of U_A/U_C at follow-up.

CONCLUSIONS Exercise testing may be useful for identifying normoalbuminuric IDDM patients who are susceptible to the later development of microalbuminuria.