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.
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.
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 r2 ≥ 0.99). There was only negligible carry-over (cyclosporine A, 0.07%) and high endurance of the solid phase extraction cartridge (>3000 injections).
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.