title: Consecutive first-morning urine samples to measure change in the albumin-to-creatinine ratio: a pilot study of a home urine collection protocol.
abstract: BACKGROUND
  Multiple first-morning urine samples are recommended for measuring the urine albumin-to-creatinine ratio (ACR); however, this can be challenging in community-based research.
  
  
  METHODS
  The objectives of the study are to pilot-test a home urine collection protocol and examine how the average and variance of ACR varied with the number of urine collections and time to laboratory analysis. This is a prospective observational pilot study. This study was conducted in London, Ontario, Canada at the London Health Sciences Centre (2012-2013). The patients were adults with chronic kidney disease (mean estimated glomerular filtration rate, 36 mL/min/1.73 m(2)). Participants collected a first-morning 20-mL urine sample on three consecutive days. This process was repeated after 3 months. Samples were picked up by hospital courier and analyzed for ACR on the same day; additional aliquots were analyzed after a delay of 24-48 h (stored at 4 °C) and 3-9 months (stored at -80 °C). The geometric mean of the percentage change in ACR between baseline and 3 months was calculated and compared between single samples and the average of two vs. three consecutive samples.
  
  
  RESULTS
  Of 31 patients enrolled, 26 (83.9 %) submitted all six urine samples. The geometric mean of ACR for three consecutive samples at baseline was 87, 83, and 80 mg/mmol, and the corresponding percentage increase from baseline to 3 months was 15 % (95 % confidence interval (CI), -9 to 46 %), 33 % (95 % CI, 10 to 59 %), and 22 % (95 % CI, -6 to 57 %). Compared with single urine collections at baseline and follow-up, averaging ACR values from two consecutive first-morning urine samples improved the sample variance and reduced the required sample size to detect a given treatment effect by approximately 30 %. No further gain in statistical efficiency was achieved with three urine samples. Results were similar when the laboratory analysis was delayed by 24-48 h, but a delay of 3-9 months resulted in systematic overestimation of the ACR. Our study's generalizability is limited by its small sample size and reliance on a clinic-based population from a single urban center.
  
  
  CONCLUSIONS
  We successfully used a home urine collection protocol to obtain multiple first-morning urine samples in patients with chronic kidney disease. Statistical efficiency was improved by averaging ACR values from two consecutive first-morning urine samples at baseline and follow-up.
authors.affiliation: Department of Epidemiology and Biostatistics, Western University, London, ON N6A 5C1 Canada ; Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Sontrop
authors.affiliation: Department of Epidemiology and Biostatistics, Western University, London, ON N6A 5C1 Canada ; Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Amit X
authors.initials: AX
authors.lastname: Garg
authors.affiliation: Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Lihua
authors.initials: L
authors.lastname: Li
authors.affiliation: Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Kerri
authors.initials: K
authors.lastname: Gallo
authors.affiliation: Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Virginia
authors.initials: V
authors.lastname: Schumann
authors.affiliation: Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Winick-Ng
authors.affiliation: Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: William F
authors.initials: WF
authors.lastname: Clark
authors.affiliation: Department of Epidemiology and Biostatistics, Western University, London, ON N6A 5C1 Canada ; Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, ON N6A 4G5 Canada.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Weir
keywords: ACR; Albumin-to-creatinine ratio; Chronic kidney disease; First-morning urine samples; Pilot study
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