B-303 Comparison of Tacrolimus Concentrations Obtained By the Newly Approved Alinity i Tacrolimus Assay With a Reference Liquid-Chromatography Combined With Tandem Mass spectrometry Assay

Abstract

Abstract Background Tacrolimus belongs to the calcineurin-inhibitor class of medications and used for preventing and maintenance of organ rejection in transplant recipients alone or in combination with other medications. Due to narrow therapeutic window and significant nephrotoxicity, this drug is routinely monitored with a suggested therapeutic range of 5–15 ng/mL. Recently, Abbott Laboratories (Abbott Park, IL) received FDA approval for using tacrolimus immunoassay on the Alinity i platform. We compared tacrolimus values in 101 transplant patients using Alinity i analyzer and a reference method based on liquid chromatography combined with mass tandem spectrometry (LC-MS/MS). Methods Tacrolimus immunoassay on the Alinity i analyzer is a chemiluminescent microparticle immunoassay (CMIA) requiring pretreatment of whole blood specimen prior to analysis. The analytical measurement range of the assay is 2–30 ng/mL. The left-over blood specimens were sent to Eurofins-Viracor reference laboratory in Lenexa, KS for analysis using LC-MS/MS method. After liquid-liquid extraction, specimens were analyzed using ascomycin as the internal standard for the presence of tacrolimus (assay is capable of analyzing other immunosuppressants simultaneously). UPLC C-18 column (waters) was used for separation using two mobile phases (A: 2.0 mM ammonium acetate in 0.1% formic caid in water and B: 2.0 mM ammonium acetate in 0.1% formic acid in methanol). Mass spectrometer was operated in positive ionization electrospray mode (tacrolimus m/z 821.6 > 768.6, ascomycin m/z 809.756.6. Results The total precision of the low control was 3.6% (mean: 4.48 ng/mL; CV 0.16 ng/mL, n = 20) while the total precision of the high control was 5.1% (mean: 25.4 ng/mL, SD: 1.29 ng/mL, n = 20). The linearity of the assay (2.0–30.0 ng/mL) was verified by running various calibrators as unknown. Comparing tacrolimus values in specimens from 101 transplant patients (49 kidney, 19 bone marrow transplant, 16 liver and 15 heart transplant) using the reference method (LC-MS/MS) as the x-axis and the corresponding values obtained by the tacrolimus immunoassay using Alinity I analyzer, we observed the following regression equation: y = 0.97 x + 1.005 (n = 101, r = 0.95). For kidney transplant recipients, the regression equation was y = 0.96 + 1.20 (n = 49, r = 0.94). Discussion Excellent correlation between tacrolimus values obtained by the newly FDA approved tacrolimus immunoassay with the reference LC-MS/MS based assay indicates further improvement in the performance of immunoassays for therapeutic drug monitoring of immunosuppressants. This may be due to reduced cross-reactivity of metabolites as indicated in the package insert. Conclusions The newly approved tacrolimus immunoassay for the application on the Alinity I analyzer can be used for routine therapeutic drug monitoring of tacrolimus in clinical laboratories.