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

Abstract

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. 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. 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. 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.