title: Paired measurement of urinary creatinine in neonates based on a Jaffe and an enzymatic IDMS-traceable assay.
abstract: BACKGROUND
  Urinary creatinine can be quantified by Jaffe or enzymatic assays and is commonly used as denominator of urinary excretion of electrolytes or protein. Paired analysis in pediatric and adult samples documented inter-assay differences (up to 80%). We verified the interchangeability of two IDMS-traceable assays (Jaffe and enzymatic) for neonatal urine and report on neonatal urinary creatinine values using these IDMS-traceable methods.
  
  
  METHODS
  Creatinine was measured in 84 neonatal urine samples from 46 neonates by an IDMS traceable Jaffe and enzymatic assay (Roche Diagnostics, Cobas c702 module). Creatinine values, differences in urinary creatinine and clinical characteristics were described and covariates of between assay difference were explored (Wilcoxon, Bland-Altman, correlation, multiple regression).
  
  
  RESULTS
  Median Jaffe and enzymatic urinary creatinine concentrations were 9.25 (range 3.7-42.2) and 9.15 (range 3.8-42.9) mg/dL respectively, resulting in a median difference of 0.08 (SD 0.6, range -2.4 to 0.96) mg/dL. In a multiple regression model, urinary enzymatic creatinine concentration (r = 0.45) and postnatal age (r = -0.59) remained independent variables of the difference between both assays (r2 adj = 0.45).
  
  
  CONCLUSIONS
  The tested IDMS-traceable assays showed interchangeable in heterogeneous neonatal urine samples. Using these assays, neonatal urinary creatinine showed 5-20 fold lower values than those observed in children or adults with a significant negative correlation with postnatal age.
authors.affiliation: Neonatal Intensive Care Unit, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium. karel.allegaert@uzleuven.be.
authors.forename: Karel
authors.initials: K
authors.lastname: Allegaert
authors.forename: Pieter
authors.initials: P
authors.lastname: Vermeersch
authors.forename: Anne
authors.initials: A
authors.lastname: Smits
authors.forename: Djalila
authors.initials: D
authors.lastname: Mekahli
authors.forename: Elena
authors.initials: E
authors.lastname: Levtchenko
authors.forename: Steven
authors.initials: S
authors.lastname: Pauwels
mesh_terms: D000465:Algorithms; D001530:Belgium; D003404:Creatinine / Q000652:urine*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D057075:Enzyme Assays / Q000379:methods* / Q000592:standards*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007677:Kidney Function Tests / Q000379:methods* / Q000592:standards*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003404:Creatinine
references.citation: Clin Chem. 1986 Feb;32(2):388-90
references.pmid: 3943207
references.citation: Ther Drug Monit. 2014 Jun;36(3):278-87
references.pmid: 24305628
references.citation: Clin Chem. 2006 Jan;52(1):5-18
references.pmid: 16332993
references.citation: Eur J Pediatr. 1996 Sep;155(9):815-9
references.pmid: 8874119
references.citation: Clin Chem. 1989 Dec;35(12):2326-30
references.pmid: 2591052
references.citation: Clin Biochem Rev. 2006 Nov;27(4):173-84
references.pmid: 17581641
references.citation: Pediatrics. 2010 May;125(5):e1186-92
references.pmid: 20368313
references.citation: Clin Chim Acta. 2004 Jun;344(1-2):137-48
references.pmid: 15149882
references.citation: Curr Pharm Des. 2012;18(21):3119-46
references.pmid: 22564304
references.citation: Pediatr Res. 2009 Jan;65(1):113-6
references.pmid: 18703997
references.citation: Arch Dis Child. 2011 Jun;96(6):575-80
references.pmid: 21317433