Comparative Evaluation of Siemens Atellica and Abbott ARCHITECT Tacrolimus Immunoassays Against LC-MS/MS: A Short...

Tacrolimus is a critical immunosuppressant that requires therapeutic drug monitoring because of its narrow therapeutic index and erratic pharmacokinetics. Although liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been deemed the "gold standard" for tacrolimus quantitation, immunoassays are widely used in practice because of their suitability for automation and their accessibility. However, interassay variability poses risks of dosing errors and therapeutic mismanagement.

The authors compared Siemens Atellica CH and Abbott ARCHITECT i2000 tacrolimus immunoassays with LC-MS/MS as the reference method. Forty whole blood samples from transplant recipients were used. The Clinical and Laboratory Standards Institute guidelines were followed for the method comparison, linearity, and precision studies. Deming regression and Bland-Altman plots were used to evaluate agreement and bias.

Both immunoassays exhibited good precision (coefficient of variation <15%) and linearity over the range established by the manufacturer. The results for both platforms correlated well with the LC-MS/MS results ( r > 0.97). The Siemens Atellica and Abbott ARCHITECT methods showed negative biases of -13.8% and -6.6%, respectively, compared with LC-MS/MS. A mean difference of -14.3% was observed between the 2 immunoassays.

Although both immunoassays met the performance standards, systematic negative bias, particularly with the Siemens Atellica method, may have affected tacrolimus dosing in the transplant recipients. Method-specific variability underscores the need for a stable monitoring platform or to re-establish the baseline during a method changeover. LC-MS/MS remains an essential method for verifying patient safety.