An automated turbulent flow liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) method for quantitation of serum creatinine

Background: When creatinine concentrations determined by routine clinical assays are in question, reference methods can aid investigation. Currently available reference methods are significantly labor-intensive, which prevents implementation in a routine clinical laboratory. Methods: Creatinine D-3 internal standard was added to serum prior to chromatographic separation. A TurboFlow® Cyclone MCX column was used for online solid phase extraction (SPE) to remove large biomolecules such as proteins, carbohydrates and phospholipids from the serum specimen. Creatinine and creatinine D-3 were then eluted onto a Hypercarb (porous graphitic carbon) column for separation. Analytes were detected using electrospray ionization tandem mass spectrometry and measured by monitoring parent ions of m/z 114 and 117, respectively. Results: Total precision at multiple levels was found to be less than 6% (1.0-7.5 mg/dl). Limit of detection (LOD) was 0.05 mg/dl and limit of quantitation (LOQ) was 0.20 mg/dl. Average recovery was 107.5% (0.37-5.95 mg/dl). Analysis of standard reference materials from The National Institute of Standards and Technology (NIST) confirmed accuracy of the method. No significant difference was found between the liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) method and the Roche Creatinine Plus enzymatic assay. Conclusion: The automated turbulent flow LC-IDMS method for quantitation of serum creatinine is accurate, robust, and easy to perform and may serve as a quick and inexpensive alternative to current creatinine reference methods.