Precision of Glucose Measurements in Control Sera by Isotope Dilution/Mass Spectrometry: Proposed Definitive Method Compared with a Reference Method

This improved isotope-dilution gas chromatographic/mass spectrometric (GC/MS) method, in which [13C]glucose is the internal standard, meets the requirements of a Definitive Method. In a first study with five reconstituted lyophilized sera, a nested analysis of variance of GC/MS values indicat-ed considerable among-vial variation. The CV for 32 mea-surements per serum ranged from 0.5 to 0.9%. However, concentration and uncertainty values (mmol/L per gram of serum) assigned to one serum by the NBS Definitive Method (7.56 ±0.28) were practically identical to those obtained with the proposed method (7.57 ±0.20). In the second study, we used twice more [13Cjglucose diluent to assay four serum pools and two lyophilized sera. The CV ranged from 0.26 to 0.5 % for the serum pools and from 0.28 to 0.59 % for the Iyoptiilized sera. In comparison, results by the hexokinase