Urine Albumin-to-Creatinine Ratio (ACR) in the First Morning Void: Influence of Collection time and Urine Retention time

Abstract

Albuminuria has been linked to the onset and progression of chronic kidney disease (CKD) and adverse cardiovascular outcomes. The Within-subject biological variability for albuminuria is estimated to range from 4% to 103%, this variability is largely dependent on the type of urine sample and the circadian proteinuria’s. To determine the effect of time of day of sample collection of first morning voids, we analyzed the equivalence of the albumin dosage and Albumin-to-creatinine ratio (ACR) in a 12-h urine sample with the ACR in a first morning urine sample collected at different times of day, which were collected between 3:50 and 5:59 a.m., 6:00 and 6:29 a.m., and 6:30 and 8:15 a.m. 123 adult participants from ELSABrasil cohort were asked to provide both a 12-h urine sample and a first morning urine sample and to record their collection times. Statistical analysis was performed using the intraclass coefficient correlation (ICC), Pearson’s r correlation coefficient, the Lin’s concordance correlation coefficient, and the Bland-Altman agreement method. Compared
to ACR obtained from 12-h overnight urine samples, ACR in samples collected between 6:30 and 8:15 a.m. of first morning void urine yielded the highest correlation coefficients (Lin’s > 0.95, Pearson’s r > 0.97, ICC >0,98) and agreement by the Bland-Altman method. The albuminuria is affected by the circadian rhythm and our results suggest that albumin and ACR measurements were significantly affected by the hour of sample collection of morning, whose collection, when it occurred between 06:30 and 08:15, showed the best agreement.