Objective: The aim of this study was the evaluation of the first commercially available in-vitro diagnostic (IVD)- mass spectrometric immunosuppressant assay from Chromsystems (MassTox Immunosuppressants ONEMINUTE Test) and the comparison to a routinely used online solid phase extraction liquid chromatography-tandem mass spectrometric assay method for the measurement of cyclosporine A, everolimus, sirolimus, and tacrolimus in patient whole blood samples.
Methods: An API 4000 [tandem mass spectrometer (AB SCIEX)] combined with a CTC Pal autosampler (CTC Analytics AG) and a Shimadzu ultra-fast liquid chromatography (UFLC) system were applied for the direct liquid chromatography-tandem mass spectrometric assay analysis using electrospray ionization in positive ion mode. Isotope-labeled internal standards were used for the commercial assay. Within- and between-day variation, accuracy, and limits of quantification were determined. Samples from external international proficiency testing schemes were measured to assess the accuracy of the commercial assay. About 100 patient samples were reanalyzed with the commercial test kit, and the results were compared with our in-house results.
Results: The limit of quantification for the commercial assay was 0.5 ng/mL for everolimus, sirolimus, and tacrolimus and 5 ng/mL for cyclosporine A. The coefficient of variation for all immunosuppressants was lower than 7% (within day) and 12% (between days) for all 5 concentration levels. Accuracy ranged between 82% and 111% for quality control samples and between 89% and 112% for samples from the external quality assurance program. Both methods showed a very good agreement (r > 0.91) in patient samples over the whole concentration range for all immunosuppressants.
Conclusion: The commercial immunosuppressant assay from Chromsystems represents a standardized IVD-certified alternative to our in-house developed assay.