title: Determination of creatinine in human urine with flow injection tandem mass spectrometry.
abstract: OBJECTIVE
  Excretion of urinary compounds in spot urine is often estimated relative to creatinine. For the growing number of liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays of urine-excreted molecules, a fast and accurate method for determination of creatinine is needed.
  
  
  METHODS
  A high-throughput flow injection tandem mass spectrometry method for exact quantitation of creatinine in urine has been developed and validated. Sample preparation used only two-step dilution for protein precipitation and matrix dilution. Flow injection analysis without chromatographic separation allowed for total run times of 1 min per sample. Creatinine concentrations were quantitated using stable isotope dilution tandem mass spectrometry. Selectivity and coelution-free quantitation were assured by qualifier ion monitoring.
  
  
  RESULTS
  Method validation revealed excellent injection repeatability of 1.0% coefficient of variation (CV), intraday precision of 1.2% CV and interday precision of 2.4% CV. Accuracy determined from standard addition experiments was 106.1 ± 3.8%. The linear calibration range was adapted to physiological creatinine concentrations. Comparison of quantitation results with a routinely used method (Jaffé colorimetric assay) proved high agreement (R(2) = 0.9102).
  
  
  CONCLUSIONS
  The new method is a valuable addition to the toolbox of LC-MS/MS laboratories where excretion of urinary compounds is studied. The 'dilute and shoot' approach to isotope dilution tandem mass spectrometry makes the new method highly accurate as well as cost- and time-efficient.
authors.affiliation: Division of Metabolic and Nutritional Medicine, Dr. von Hauner Children's Hospital, University of Munich Medical Centre, Munich, Germany.
authors.forename: Mareile
authors.initials: M
authors.lastname: Niesser
authors.forename: Berthold
authors.initials: B
authors.lastname: Koletzko
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Peissner
mesh_terms: D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002853:Chromatography, Liquid / Q000379:methods; D003124:Colorimetry / Q000379:methods; D003404:Creatinine / Q000652:urine*; D006801:Humans; D007201:Indicator Dilution Techniques / Q000295:instrumentation*; D012015:Reference Standards; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D003404:Creatinine