title: Day-to-day variability in spot urine protein-creatinine ratio measurements.
abstract: BACKGROUND
  Accurate measurement of proteinuria is important in the diagnosis and management of chronic kidney disease (CKD). The reference standard test, 24-hour urinary protein excretion, is inconvenient and vulnerable to collection errors. Spot urine protein-creatinine ratio (PCR) is a convenient alternative and is in widespread use. However, day-to-day variability in PCR measurements has not been evaluated.
  
  
  METHODS
  Prospective cohort study of day-to-day variability in spot urine PCR measurement.
  
  
  METHODS
  Clinically stable outpatients with CKD (n = 145) attending a university hospital CKD clinic in Australia between July 2007 and April 2010.
  
  
  METHODS
  Spot urine PCR.
  
  
  RESULTS
  Spot PCR variability was assessed and repeatability limits were determined using fractional polynomials.
  
  
  METHODS
  Spot PCRs were measured from urine samples collected at 9:00 am on consecutive days and 24-hour urinary protein excretion was collected concurrently.
  
  
  RESULTS
  Paired results were analyzed from 145 patients: median age, 56 years; 59% men; and median 24-hour urinary protein excretion, 0.7 (range, 0.06-35.7) g/d. Day-to-day variability was substantial and increased in absolute terms, but decreased in relative terms with increasing baseline PCR. For patients with a low baseline PCR (20 mg/mmol [177 mg/g]), a change greater than ±160% (repeatability limits, 0-52 mg/mmol [0-460 mg/g]) is required to indicate a real change in proteinuria status with 95% certainty, whereas for those with a high baseline PCR (200 mg/mmol [1,768 mg/g]), a change of ±50% (decrease to <100 mg/mmol [<884 mg/g] or increase to >300 mg/mmol [>2,652 mg/g]) represents significant change.
  
  
  CONCLUSIONS
  These study results need to be replicated in other ethnic groups.
  
  
  CONCLUSIONS
  Changes in PCR observed in patients with CKD, ranging from complete resolution to doubling of PCR values, could be due to inherent biological variation and may not indicate a change in disease status. This should be borne in mind when using PCR in the diagnosis and management of CKD.
authors.affiliation: Department of Renal Medicine, The Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
authors.forename: Chetana N
authors.initials: CN
authors.lastname: Naresh
authors.forename: Andrew
authors.initials: A
authors.lastname: Hayen
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Craig
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Chadban
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011507:Proteinuria / Q000175:diagnosis*; D012015:Reference Standards; D051436:Renal Insufficiency, Chronic / Q000175:diagnosis*; D015203:Reproducibility of Results; D059349:Urine Specimen Collection; D055815:Young Adult
chemical_list: D003404:Creatinine