Evaluation of albumin excretion rate in overnight versus 24-h urine

This study was performed to assess whether the albumin excretion rate (AER) measured in overnight urine (N-AER) and 24-h urine (24-h AER) gives comparable results. For this reason we evaluated N-AER and 24-h AER on the same day from 35 control subjects, 57 patients with insulin-dependent diabetes mellitus (IDDM), and 63 patients with non-insulin-dependent diabetes mellitus (NIDDM). AER values obtained from the two urine collection procedures were significantly different (P less than .01), with 24-h AER approximately 30% higher than N-AER. Moreover, when the same cutoff value (20 micrograms/min) was used to define the normal range, 21% of IDDM patients and 6.3% of NIDDM patients had on the same day normal N-AER and abnormal (greater than 20 micrograms/min) 24-h AER. Although N-AER values were significantly correlated to 24-h AER values (r = 0.67, P less than .001), it was not possible to assess an N-AER value able to predict a 24-h AER value greater than 20 micrograms/min. In conclusion, N-AER and 24-h AER cannot be used as an equivalent method to establish AER.