Analytical performance characteristics of the Abbott Architect i2000 Tacrolimus assay; comparisons with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and Abbott IMx methods

BackgroundTacrolimus, an immunosuppressive drug discovered in 1984, is used to decrease the risk of organ rejection. The 2007 European Consensus Conference on Tacrolimus Optimization recommended the use of methods with a limit of quantitation at ≤ 1 ng/ml for monitoring low dose tacrolimus therapy.MethodsThe performance characteristics of the Abbott i2000 Tacrolimus assay were evaluated and compared to LC-MS/MS and Abbott IMx methods.ResultsThe limit of detection of the Abbott i2000 method was 0.21 ng/ml. Total imprecision was 6.9, 5.8 and 4.2% at three target concentrations of tacrolimus (3.2, 8.5 and 15.9 ng/ml) respectively. The method was linear up to 30 ng/ml. The limit of quantitation (LOQ) was 0.5 ng/ml. Correlation of patient specimen results between the Abbott i2000 method and LC-MS/MS yielded a Deming slope of 1.072 ng/ml (CI 1.005 to 1.140), r = 0.952 and an intercept of − 0.491 ng/ml (CI −1.387 to 0.405). The mean bias, as determined by Bland–Altman analysis, was 0.36 ng/ml. Comparing results generated by the widely used Abbott IMx assay with LC-MS/MS and Architect i2000 methods yielded Deming slopes of 1.062 and 0.973, with intercepts of − 0.214 ng/ml and − 0.01 ng/ml respectively. For both comparisons, r = 0.97. The corresponding mean bias of results generated by the Abbott IMx assay (Bland–Altman plots) was 0.53 ng/ml vs LC-MS/MS and − 0.38 ng/ml vs the Architect i2000.ConclusionsThe Architect i2000 method is a sensitive and highly precise method that achieves a LOQ of < 1.0  ng/ml and demonstrated overall accuracy of tacrolimus measurements within 0.4 ng/ml.