Background: Sirolimus (SRL) is a macrocyclic lactone, indicated for prevention of organ rejection after kidney transplantation. Therapeutic drug monitoring of this agent constitutes an important part to immunosuppressive treatment because of its narrow window of therapeutic efficacy. Routine methods include manual pretreatment of samples. The aim of this study was to evaluate the performance characteristics of an automated immunoassay that does not require manual pretreatment to quantify SRL in whole blood on the Dimension analyzer.
Methods: We examined 50 whole blood samples collected routinely from kidney transplant patients treated with SRL. The samples were analyzed simultaneously by an immunoassay on an IMx analyzer (reference method), which requires manual pretreatment step versus a totally automated immunoassay on the Dimension analyzer, which does not require this pretreatment.
Results: The Dimension SRL assay had a functional sensitivity of ≤2.4 ng/mL. Total imprecision was 15.6% at a concentration of 2.8 ng/mL; 10% at 7.9 ng/mL; and 5.2% at 18.4 ng/mL. Least-squares linear regression analysis yielded an r-value of 0.973 with the following equation: SRL-D=1.204*SRL-IMx-0.251. Bland-Altman comparison showed a mean positive difference of 1.38 ng/mL (95% confidence interval, -1.10 to 3.82), namely, 17.2% for SRL Dimension. The Dimension assay to monitor SRL concentrations was an acceptable method for routine clinical use, with total assay imprecision (%CV) ranging from 10.0% to 5.2% within and above the therapeutic concentration range, respectively.
Conclusion: SRL IMx and Sirolimus Dimension methods show a good correlation (r=0.973), but the SRL Dimension method demonstrated a positive average difference of 17.2% compared with the IMx method. The Dimension assay to monitor whole blood SRL concentration does not require a manual pretreatment step, reducing turnaround time and making this method an attractive alternative for SRL analysis.
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