Immunosuppressive drugs in whole blood : validation of a commercially available LC-MS/MS kit and comparison with immunochemical assays

RATIONALE: In the determination of immunosuppressive drugs cyclosporine A (CSA), tacrolimus (TARO), sirolimus (SIRO), and everolimus (EVE) in whole blood there is an open debate about which is the best assay between immunochemistry and liquid chromatography/tandem mass spectrometry (LC/MS/MS). This work is aimed to explore this topic, focusing on the use of updated assays and the analysis of a large number of samples. METHODS: A certified in vitro diagnostic kit coupled with a medical device LC/MS/MS was validated and applied to the analysis of 1192 blood samples of patients treated with immunosuppressive drugs. The results were compared with those obtained by immunoassays. RESULTS: The LC/MS/MS approach was found to provide linear, stable, precise, and accurate results, with lower limits of quantification of 12.5, 1.1, 1.2, and 1.2 μg/L for CSA, TACRO, SIRO, and EVE, respectively. With this method 80 samples were analysed and reported within a single work shift. A correlation was observed between the LC/MS/MS and immunoassay data, with Spearman correlation coefficients of 0.980 (n = 260) for CSA, 0.836 for TACRO (n = 562), 0.898 for SIRO (n = 113), and 0.904 for EVE (n = 257). Passing-Bablock regression showed the presence of constant and proportional biases for most of the drugs. A Blond-Altman graph showed differences between the assays, with immunoassays generally overestimating the drugs. CONCLUSIONS: The LC/MS/MS certified kit was validated for the detection of immunosuppressant drugs in whole blood and it provided a high-throughput method that is consistent with the requirements of clinical laboratories. The comparison of patient data between LC/MS/MS and up-dated immunoassays shows that a significant discrepancy still exists, especially for CSA and SIRO, confirming the greater specificity associated with use of the LC/MS/MS assay.