A liquid chromatography-tandem mass spectrometry-based candidate reference measurement procedure for the...

Vancomycin is a glycopeptide antibiotic used to treat severe Gram-positive infections; its narrow therapeutic window makes therapeutic drug monitoring (TDM) critical. We report the development of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) candidate reference measurement procedure (RMP) to quantify vancomycin in human plasma and serum.

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was used to determine the absolute content of the reference material, ensuring direct traceability to the International System of Units (SI). Sample preparation used a protein precipitation protocol followed by high dilution. LC-MS/MS parameters, including selectivity, precision, accuracy, equivalence to the listed RMP, and measurement uncertainty (MU) were evaluated. MU determination was performed according to the guide to the expression of uncertainty in measurement (GUM).

The RMP was validated over a measuring interval of 0.690-58.7 μmol/L (1.00-85.0 μg/mL). Intermediate precision and repeatability were <2.9 % and <2.1 %, respectively. Direct comparison with the current JCTLM-listed RMP revealed an 18.3 % downward shift in results. This bias was proven to be entirely attributable to the transition from activity-based to mass-based standardization. Expanded MU (k=2) ranged from 5.1 % to 6.0 % for single measurements and 2.1-3.1 % for target value assignment.

This candidate RMP provides a superior metrological foundation for vancomycin quantification by establishing direct SI-traceability and a fully characterized uncertainty budget. While its implementation necessitates a re-evaluation of clinical decision thresholds, it significantly enhances the global standardization of TDM assays.