Determination of serum creatinine by isotope dilution liquid chromatography tandem mass spectrometry: a candidate reference method

Objective To develop a candidate reference method for the measurement of creatinine in human serum based on isotope dilution liquid chromatography tandem mass spectrometry (ID-LC/MS/MS). Methods An isotopically labeled internal standard [ H ] creatinine was added to the serum sample and equilibrated with the endogenous creatinine. The samples were treated with anhydrous ethanol to remove proteins by precipitation. After being washed with chloroform for further clean-up, the samples were analyzed by LC/MS/MS. Serum creatinine was quantified by a bracketing calibration. Results The within-run, between-run and total coefficients of variation ranged from 0.52% to 0.61%, 0.11% to 0.59% and 0.61% to 0.83%, and the averages were 0.57%, 0.43% and 0.73%, respectively. The analytical recoveries ranged from 99.09% to 101.13% with an average of 100.3%.The results of analyzing the certified reference material SRM 909b (Level Ⅰ and Ⅱ) and SRM 967b showed biases of less than 0.4%. Conclusions An ID-LC/MS/MS method for measuring serum creatinine has been developed. The method is highly precise and accurate and may be used as a candidate reference method for serum creatinine measurements. Key words: Creatinine;  Isotope labeling;  Chromatography,liquid;  Tandem mass spectrometry