title: Effect of Processing Delay and Storage Conditions on Urine Albumin-to-Creatinine Ratio.
abstract: Because there is substantial biologic intraindividual variation in albumin excretion, randomized trials of albuminuria-reducing therapies may need multiple urine samples to estimate daily urinary albumin excretion. Mailing spot urine samples could offer a convenient and cost-effective method to collect multiple samples, but urine albumin-to-creatinine ratio stability in samples stored at ambient temperatures for several days is unknown.
  
  
  
  Patients with kidney disease provided fresh urine samples in two tubes (with and without boric acid preservative). Reference aliquots from each participant were analyzed immediately, whereas remaining aliquots were subject to different handling/storage conditions before analysis, including delayed processing for up to 7 days at three different storage temperatures (4°C, 18°C, and 30°C), multiple freeze-thaw cycles, and long-term frozen storage at -80°C, -40°C, and -20°C. We calculated the mean percentage change in urine albumin-to-creatinine ratio for each condition, and we considered samples stable if the 95% confidence interval was within a ±5% threshold.
  
  
  
  Ninety-three patients provided samples with detectable albuminuria in the reference aliquot. Median (interquartile range) urine albumin-to-creatinine ratio was 87 (20-499) mg/g. The inclusion of preservative had minimal effect on fresh urine albumin-to-creatinine ratio measurements but reduced the changes in albumin and creatinine in samples subject to processing delay and storage conditions. The urine albumin-to-creatinine ratio was stable for 7 days in samples containing preservative at 4°C and 18°C and 2 days when stored at 30°C. It was also stable in samples with preservative after three freeze-thaw cycles and in frozen storage for 6 months at -80°C or -40°C but not at -20°C.
  
  
  
  Mailed urine samples collected with preservative and received within 7 days if ambient temperature is ≤18°C, or within 2 days if the temperature is higher but does not exceed 30°C, are suitable for the measurement of urine albumin-to-creatinine ratio in randomized trials. Preserved samples frozen to -40°C or -80°C for 6 months before analysis also seem suitable.
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Oxford Kidney Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and.
authors.forename: William
authors.initials: W
authors.lastname: Herrington
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Nicola
authors.initials: N
authors.lastname: Illingworth
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Natalie
authors.initials: N
authors.lastname: Staplin
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Aishwarya
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Oxford Kidney Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Ben
authors.initials: B
authors.lastname: Storey
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Renata
authors.initials: R
authors.lastname: Hrusecka
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Oxford Kidney Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Parminder
authors.initials: P
authors.lastname: Judge
authors.affiliation: Oxford Kidney Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and.
authors.forename: Maria
authors.initials: M
authors.lastname: Mahmood
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Parish
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Landray
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Oxford Kidney Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Haynes
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Colin
authors.initials: C
authors.lastname: Baigent
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Hill
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, Oxford, United Kingdom.|Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, Oxford, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Clark
mesh_terms: D000328:Adult; D000368:Aged; D000419:Albuminuria / Q000209:etiology / Q000652:urine*; D001888:Boric Acids; D003404:Creatinine / Q000652:urine*; D005260:Female; D005615:Freezing; D006801:Humans; D007674:Kidney Diseases / Q000150:complications / Q000652:urine*; D008297:Male; D008875:Middle Aged; D013048:Specimen Handling / Q000379:methods*; D013696:Temperature; D013997:Time Factors; D059349:Urine Specimen Collection
chemical_list: D001888:Boric Acids; D003404:Creatinine; C032688:boric acid
keywords: Albumins; Boric Acids; Confidence Intervals; Freezing; Humans; Kidney Diseases; Randomized Controlled Trials as Topic; Specimen Handling; Temperature; Urinalysis; albuminuria; boric acid; creatinine; microalbuminuria; proteinuria; randomized controlled trials