title: Day-to-day variability in spot urine albumin-creatinine ratio.
abstract: BACKGROUND
  Accurate quantification of albuminuria is important in the diagnosis and management of chronic kidney disease. The reference test, a timed urinary albumin excretion, is cumbersome and prone to collection errors. Spot urine albumin-creatinine ratio (ACR) is convenient and commonly used, but random day-to-day variability in ACR measurements has not been assessed.
  
  
  METHODS
  Prospective cohort study of day-to-day variability in spot urine ACR measurements.
  
  
  METHODS
  Clinically stable outpatients (N = 157) attending a university hospital clinic in Australia between July 2007 and April 2010.
  
  
  RESULTS
  Spot urine ACR variability was assessed and repeatability limits were determined using fractional polynomials.
  
  
  METHODS
  ACRs were measured from spot urine samples collected at 9:00 am on consecutive days and 24-hour urine albuminuria was measured concurrently.
  
  
  RESULTS
  Paired ACRs were obtained from 157 patients (median age, 56 years; 60% men; median daily albumin excretion, 226 [range, 2.5-14,000] mg/d). Day-to-day variability was substantial and increased in absolute terms, but decreased in relative terms, with increasing baseline ACR. For patients with normoalbuminuria (ACR < 3 mg/mmol [<27 mg/g]), a change greater than ±467% (0-17 mg/mmol [0-150 mg/g]) is required to indicate a significant change in albuminuria status with 95% certainty; for those with microalbuminuria (ACR of 3-30 mg/mmol [27-265 mg/g]), a change of ±170% (0-27 mg/mmol [0-239 mg/g]) is required; for those with macroalbuminuria (ACR > 30 mg/mmol [>265 mg/g]), a change of ±83% (5-55 mg/mmol [44-486 mg/g]) is required; and for those with nephrotic-range proteinuria (ACR > 300 mg/mmol [>2,652 mg/g]), a change of ±48% (158-443 mg/mmol [1,397-3,916 mg/g]) is needed to represent a significant change.
  
  
  CONCLUSIONS
  These study results need to be replicated in other ethnic groups.
  
  
  CONCLUSIONS
  Changes in chronic kidney disease status attributed to therapy or disease progression, when based solely on a change in ACR, may be incorrect unless the potential for day-to-day biological variation has been considered. Only relatively large changes are likely to indicate a change in disease status.
authors: Department of Renal Medicine, The Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia; Sydney Medical School, University of Sydney, Sydney, Australia.
authors: Chetana N
authors: CN
authors: Naresh
authors: Andrew
authors: A
authors: Hayen
authors: Alexander
authors: A
authors: Weening
authors: Jonathan C
authors: JC
authors: Craig
authors: Steven J
authors: SJ
authors: Chadban
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000419:Albuminuria / Q000175:diagnosis / Q000652:urine*; D000704:Analysis of Variance; D002940:Circadian Rhythm; D015331:Cohort Studies; D003404:Creatinine / Q000652:urine*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000652:urine*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D009404:Nephrotic Syndrome / Q000175:diagnosis / Q000652:urine; D009517:New South Wales; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012016:Reference Values; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D003404:Creatinine
keywords: Albuminuria; albumin-creatinine ratio; chronic kidney disease; proteinuria