41. Method Comparison of Immunosuppressant Quantitation: Abbott ARCHITECT versus LC-MS/MS
Poster: Tue 2:00-3:00PM
Jonathan Hoyne
Mayo Clinic
Jonathan B. Hoyne, Mayo Clinic, Jacksonville, Fl.
Sirolimus and Tacrolimus are immunosuppressive drugs used after organ transplant to inhibit transplant rejection by the host. Their pharmacokinetic profiles exhibit significant inter-individual variability. Sub-therapeutic concentrations may result in graft rejection while supra-therapeutic concentrations may lead to nephrotoxicity. For these reasons therapeutic drug monitoring of these immunosuppressants is the standard of care for post-transplant patients. In order to determine the relative analytical performance of the Abbott immunoassays versus an LC-MS/MS method, we conducted a method comparison between split samples run on the ARCHITECT i2000sr and on an ABI-4000 LC-MS/MS

We ran whole blood samples from patients being treated in our transplant center and receiving sirolimus or tacrolimus. Split samples that were not run immediately were frozen and stored at -20C. For quantitation by LC-MS/MS 0.5 mLs of sample was added to 70/30 water/methanol containing 26 mg/mL zinc sulfate and 50 ng/mL ascomycin for internal standard. Samples were vortexed vigorously then centrifuged for 10 minutes at 3000 rpm to remove insoluble material. 200 uL of supernatant were injected by a LEAP HTC-PAL autosampler and loaded onto a 3 μm Phenomenex Securityguard C-8 cartridge (AJO-4290) with 20 mM ammonium acetate in 50/50 methanol/water at 3 mL/min. Analyte was eluted with 20 mM ammonium acetate in 90/10 methanol/water at 1 mL/min. Daughter ions for analyte and internal standard were detected in MRM mode on an ABI 4000 and quantified accordingly. Samples were prepared and analyzed on an Abbott ARCHITECT i2000sr in accordance with manufacturer’s instructions.

Comparisons between results obtained by the two methods for tacrolimus were efficiently modeled by linear regression (y= 1.0305x + 0.6861; r2 = 0.9543). The values for sirolimus as assessed by both methods showed good agreement (y = 1.0012x + 1.29 ). However, the variation between methods was confounded by unexplained factors as the r2 value between methods was < 0.95 (r2 = 0.9028). This may be due to cross reactivity of metabolite in the Architect immunoassay.

We thank Veronica Harrison from Abbott Diagnostics for preparing and running split samples from our laboratory on an ARCHITECT i2000sr. In addition, Abbott Diagnostics provided reagents necessary to run these samples. Abbott Diagnostics did not provide any monetary support for this study, nor did they participate in review or analysis of the data.
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