Development and validation of a rapid liquid chromatography isotope dilution tandem mass spectrometry (LC-IDMS/MS) method for serum creatinine

Objectives:To develop an isotope dilution liquid chromatography tandem mass spectrometry (LC-IDMS/MS) method for the standardization of serum creatinine.Design and methods:Supernatants obtained by protein precipitation were injected into a LC-MS/MS. Chromatography was performed on a cation exchanger pre-column in normal phase isocratic mode. Creatinine and creatinine-D3 were quantified using ion transitions of m/z 114→44 and 117→47, respectively.Results:The method was calibrated with the NIST Standard Reference Material 914a and was found to be exact in analyzing the certified reference material SRM 967 from NIST (97.1 ± 0.9% and 102.1 ± 0.9% of target value for levels 1 and 2, respectively) and by calculating recuperation of spiked creatinine in 10 different patient samples (103.6 ± 4.1%). Intra-assay imprecision was 0.9% at both 64.6 and 354 μmol/L creatinine, while inter-assay imprecisions were 1.9% and 1.8%. Absence of ion suppression was confirmed by spiking experiments. The method was shown to be free of carryover. A good correlation was obtained between the LC-MS/MS method and a Jaffe method run on an automated analyzer (r = 0.999).Conclusions:We have developed a fast and simple method for the quantification of serum creatinine by isotope dilution tandem mass spectrometry (IDMS/MS) and we propose that this method can be used as a reference method by laboratories that wish to validate their serum creatinine automated assay.