Background: Typical runtimes for quantitation of immunosuppressants in whole blood based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) are in the order of a few minutes per sample. The Agilent RapidFire-MS/MS system uses solid phase extraction cartridges instead of chromatography columns and benefits from runtimes below 15 seconds. The purpose of this study was to figure out if this high-throughput instrument could be capable for application in the clinical laboratory to quantify cyclosporine A, everolimus, sirolimus, and tacrolimus.
Methods: 1172 measurement results from patient samples were compared between our routinely used LC-MS/MS system and the RapidFire 360 coupled to a tandem mass spectrometer. Sample preparation and routine measurement were performed using a certified kit. Imprecision and accuracy were investigated analyzing 3 commercial quality controls of different concentrations.
Results: Both measurement procedures showed excellent agreement (Pearson correlation coefficients r = 0.964-0.995). Deming regression revealed confidence intervals (95%) for slopes and intercepts of the linear equation, which covered the values 1 and 0, respectively, in almost all cases. The relative differences between both methods were marginal (1.7%-2.9%). Good intraday precision (coefficients of variation, 0.7%-9.0%) and interday precision (coefficients of variation, 2.8%-8.4%) for all immunosuppressants were achieved. The recovery of target concentrations was 81%-116%. High robustness was found with regard to linearity of the calibration lines (linear regression coefficients r ≥ 0.99). There was only negligible carry-over (cyclosporine A, 0.07%) and high endurance of the solid phase extraction cartridge (>3000 injections).
Conclusions: The RapidFire-MS/MS system provided convincing results measuring patient samples and quality control materials. Together with a high throughput and a high robustness, it could represent an alternative to LC-MS/MS instruments in therapeutic drug monitoring.