title: Urinary albumin excretion in healthy adults: a cross sectional study of 24-hour versus timed overnight samples and impact of GFR and other personal characteristics.
abstract: BACKGROUND
  Urinary albumin can be measured in 24 h or spot samples. The 24 h urinary albumin excretion rate is considered the gold standard, but is cumbersome to collect. Instead, often an overnight sample is collected, and adjusted for dilution. Proxies for 24 h excretion rate have been studied in diabetics, but seldom in healthy individuals. Our aims were to compare 24 h and overnight albumin excretion, to assess the impact of personal characteristics, and to examine correlations between the 24 h excretion rate and proxies such as the albumin to creatinine ratio (ACR).
  
  
  METHODS
  Separate 24 h and overnight urine samples were collected from 152 healthy kidney donors. Urinary creatinine, specific gravity, collection time, and sample volume determined. Differences between 24 h and overnight samples were examined, and the effects of age, sex, smoking, body mass, glomerular filtration rate, and urinary flow rate were assessed.
  
  
  RESULTS
  The 24 h albumin excretion rate and ACR were both significantly higher than their overnight counterparts. Unadjusted albumin was unsurprisingly higher in the more concentrated overnight samples, while concentrations adjusted for specific gravity were similar. In multivariate analysis, the 24 h excretion rate and proxies were positively associated with glomerular filtration rate, as was ACR in overnight samples. There were positive associations between urinary albumin and body mass.
  
  
  CONCLUSIONS
  Proxies for the 24 h albumin excretion rate showed relatively high correlations with this gold standard, but differences due to sampling period, adjustment method, and personal characteristics were large enough to be worth considering in studies of albumin excretion in healthy individuals.
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska Academy, University of Gothenburg, PO Box 414, Gothenburg, S-405 30, Sweden. peter.fagerstrom@amm.gu.se.
authors.forename: Peter
authors.initials: P
authors.lastname: Fagerstrom
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska Academy, University of Gothenburg, PO Box 414, Gothenburg, S-405 30, Sweden. gerd.sallsten@amm.gu.se.
authors.forename: Gerd
authors.initials: G
authors.lastname: Sallsten
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska Academy, University of Gothenburg, PO Box 414, Gothenburg, S-405 30, Sweden. magnus.akerstrom@amm.gu.se.
authors.forename: Magnus
authors.initials: M
authors.lastname: Akerstrom
authors.affiliation: Department of Molecular and Clinical Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. borje.haraldsson@gu.se.
authors.forename: Borje
authors.initials: B
authors.lastname: Haraldsson
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska Academy, University of Gothenburg, PO Box 414, Gothenburg, S-405 30, Sweden. lars.barregard@amm.gu.se.
authors.forename: Lars
authors.initials: L
authors.lastname: Barregard
mesh_terms: D000328:Adult; D000368:Aged; D000419:Albuminuria / Q000652:urine*; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000502:physiology*; D019520:Living Donors; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D059349:Urine Specimen Collection; D055815:Young Adult