title: Utilizing Estimated Creatinine Excretion to Improve the Performance of Spot Urine Samples for the Determination of Proteinuria in Kidney Transplant Recipients.
abstract: BACKGROUND
  Agreement between spot and 24-hour urine protein measurements is poor in kidney transplant recipients. We investigated whether using formulae to estimate creatinine excretion rate (eCER), rather than assuming a standard creatinine excretion rate, would improve the estimation of proteinuria from spot urine samples in kidney transplant recipients.
  
  
  METHODS
  We measured 24 hour urine protein and albumin and spot albumin:creatinine (ACR) and spot protein:creatinine (PCR) in 181 Kidney transplant recipients." We utilized 6 different published formulae (Fotheringham, CKD-EPI, Cockcroft-Gault, Walser, Goldwasser and Rule) to estimate eCER and from it calculated estimated albumin and protein excretion rate (eAER and ePER). Bias, precision and accuracy (within 15%, 30% and 50%) of ACR, PCR, eAER, ePER were compared to 24-hour urine protein and albumin.
  
  
  RESULTS
  ACR and PCR significantly underestimated 24-hour albumin and protein excretion (ACR Bias (IQR), -5.9 mg/day; p< 0.01; PCR Bias, (IQR), -35.2 mg/day; p<0.01). None of the formulae used to calculate eAER or ePER had a bias that was significantly different from the 24-hour collection (eAER and ePER bias: Fotheringham -0.3 and 7.2, CKD-EPI 0.3 and 13.5, Cockcroft-Gault -3.2 and -13.9, Walser -1.7 and 3.1, Goldwasser -1.3 and -0.5, Rule -0.6 and 4.2 mg/day respectively. The accuracy for ACR and PCR were lower (within 30% being 38% and 43% respectively) than the corresponding values estimated by utilizing eCER (for eAER 46% to 49% and ePER 46-54%).
  
  
  CONCLUSIONS
  Utilizing estimated creatinine excretion to calculate eAER and ePER improves the estimation of 24-hour albuminuria/proteinuria with spot urine samples in kidney transplant recipients.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Canada.
authors.forename: Michael Ke
authors.initials: MK
authors.lastname: Wang
authors.affiliation: Division of Nephrology, Department of Medicine, Queens University, Kingston, Canada.
authors.forename: Christine
authors.initials: C
authors.lastname: White
authors.affiliation: Division of Nephrology, Department of Medicine, University of Ottawa, Ottawa, Canada.|Kidney Research Centre, University of Ottawa, Ottawa, Canada.|Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada.
authors.forename: Ayub
authors.identifier: http://orcid.org/0000-0002-1388-9799
authors.initials: A
authors.lastname: Akbari
authors.affiliation: Division of Nephrology, Department of Medicine, University of Ottawa, Ottawa, Canada.|Kidney Research Centre, University of Ottawa, Ottawa, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Brown
authors.affiliation: Division of Nephrology, Department of Medicine, Mubarak AlKabeer Hospital, Kuwait City, Kuwait.
authors.forename: Naser
authors.initials: N
authors.lastname: Hussain
authors.affiliation: Division of Nephrology, Department of Medicine, University of Ottawa, Ottawa, Canada.|Kidney Research Centre, University of Ottawa, Ottawa, Canada.|Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada.
authors.forename: Swapnil
authors.initials: S
authors.lastname: Hiremath
authors.affiliation: Division of Nephrology, Department of Medicine, University of Ottawa, Ottawa, Canada.|Kidney Research Centre, University of Ottawa, Ottawa, Canada.|Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada.
authors.forename: Greg
authors.initials: G
authors.lastname: Knoll
mesh_terms: D000368:Aged; D000419:Albuminuria / Q000209:etiology / Q000652:urine*; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged
chemical_list: D003404:Creatinine