Stability of creatinine with delayed separation of whole blood and implications for eGFR

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...