title: Stability of creatinine with delayed separation of whole blood and implications for eGFR.
abstract: BACKGROUND
  The stability of creatinine in whole blood is unclear: it is not known if analysis of creatinine in samples with delayed separation could lead to misclassification of chronic kidney disease (CKD) using estimated glomerular filtration rate (eGFR).
  
  
  METHODS
  Multiple blood samples were taken at a single time-point from five individuals and subject to varying time delays prior to centrifugation, after which serum was separated and analysed for creatinine by five different methods. The effect of time delay on eGFR was further investigated by measuring creatinine on duplicate patient samples arriving in the laboratory after immediate and delayed centrifugation.
  
  
  RESULTS
  A significant increase in creatinine was seen by 24 h using kinetic Jaffe methods (P<0.025). Over a period of 31 h creatinine concentration was stable using enzymatic creatinine assays. Using duplicate patient samples, four of 21 patients where specimens were delayed in the laboratory by more than 10 h showed a misclassification of CKD.
  
  
  CONCLUSIONS
  Delays in sample receipt can lead to significant increases in measured creatinine and misclassification of CKD. Enzymatic creatinine assays are reliable with respect to delayed sample receipt over the time course studied.
authors.affiliation: Department of Clinical Biochemistry, Hull Royal Infirmary, Hull, UK. john.shepherd@hey.nhs.uk
authors.forename: J
authors.initials: J
authors.lastname: Shepherd
authors.forename: M H
authors.initials: MH
authors.lastname: Warner
authors.forename: E S
authors.initials: ES
authors.lastname: Kilpatrick
mesh_terms: D000328:Adult; D000368:Aged; D001800:Blood Specimen Collection; D002138:Calibration; D003404:Creatinine / Q000097:blood* / Q000302:isolation & purification; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000175:diagnosis*; D007677:Kidney Function Tests; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D003404:Creatinine