Isotope-dilution-LC-MS/MS candidate reference measurement procedure for cefepime in human serum

Background: Reference measurement procedures are an essential element in the standardization and comparability of analytical measurement results in laboratory medicine. No LC-MS/MS-based reference measurement procedure for cefepime in serum has been published previously. Materials and methods: An isotope-dilution based two-dimensional LC-MS/MS reference measurement procedure for cefepime concentrations in human serum was developed and tested. The value assignment of unknown samples is based on a defined measurement series validation. Six unknown samples can be measured per series. Pass criteria for the run and the samples were determined empirically based on a performance evaluation. For this purpose, a between-run determination of five runs of the defined measurement series with six cefepime samples was carried out and evaluated. The goal was to define rigorous, realistic target limits and minimize measurement uncertainty. The final defined target limits are used for series-based validation and value assignment. The results for the six unknown samples are provided with the associated measurement uncertainty for this series. Results: The developed and extensively studied measurement procedure for the quantification of cefepime in serum was found to be practicable and fit for its purpose. The between-run mean imprecision of the six cefepime samples was <= 2.0 %, for the QCs it was <= 2.3 % and the between-run mean inaccuracy of the QCs was within +/- 1.1 %. Conclusion: The novel isotope-dilution-LC-MS/MS measurement procedure in accordance to ISO 15193 can be recommended as candidate reference measurement procedure for the value assignment of cefepime concentrations in human serum.