title: Comparison of methods, storage conditions, and time to analysis of serum and urine creatinine measured from microsamples by liquid chromatography mass spectrometery (LC/MS) vs. Jaffe.
abstract: BACKGROUND
  Measurement of serum creatinine (SCr) and urine creatinine (UCr) is regularly used in clinical and research settings. For small animal experiments and for studies in which sample collection is spare (i.e. neonatal cohorts), measuring SCr and UCr using tiny amounts of sample (as low as 10 mcl) would maximize exploration and minimize iatrogenic blood loss.
  
  
  METHODS
  We performed an evaluation in six healthy adults to determine differences between SCr and UCr values in different methodologies and storage environments and time. Study was conducted using 20 mcl of sample. Analyses were done using two-way repeated measures of ANOVA.
  
  
  RESULTS
  Scr values showed no significant differences between LC/MS vs. Jaffe. However, the SCr using LC/MS method was lowest when measured immediately compared to other time points (F = 7.2; P< 0.001). Similarly, Jaffe measurements showed changes in the mean differences over time; however, these were not significant. UCr values were consistently higher using LC/MS than Jaffe (F = 19; P< 0.01), and UCr changed over time (F = 8.7; P < 0.02). In addition, the interaction term for method and time was also significant (F = 5.8; P < 0.04) which reflects the stability of the Jaffe measurements over time whereas the LC/MS measurements declined; especially after being frozen for 1 year (P < 0.001).
  
  
  CONCLUSIONS
  UCr measured by Jaffe is lower than samples measured by LC/MS. UCr measurements by LC/MS vary more over time, mostly due to the sample measured after 1 year; therefore, storage of urine for more than 90 days measured by LC/MS may provide altered results.
authors.affiliation: Department of Pediatrics Nephrology, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: David J
authors.initials: DJ
authors.lastname: Askenazi
authors.forename: John F
authors.initials: JF
authors.lastname: Moore
authors.forename: Naomi
authors.initials: N
authors.lastname: Fineberg
authors.forename: Rajesh
authors.initials: R
authors.lastname: Koralkar
authors.forename: Stephanie
authors.initials: S
authors.lastname: Clevenger
authors.forename: Jon Daniel
authors.initials: JD
authors.lastname: Sharer
mesh_terms: D000704:Analysis of Variance; D001774:Blood Chemical Analysis / Q000592:standards*; D002853:Chromatography, Liquid; D003404:Creatinine / Q000097:blood* / Q000652:urine*; D015925:Cryopreservation; D006801:Humans; D013058:Mass Spectrometry; D013048:Specimen Handling / Q000592:standards*; D013997:Time Factors; D016482:Urinalysis / Q000592:standards*
chemical_list: D003404:Creatinine
keywords: creatinine