B-175 Comparative analysis of two methods for the determination of tacrolimus in whole blood

Background Introduction Tacrolimus is an immunosuppressive drug from the calcineurin inhibitors group. It works by inhibiting the activation of T lymphocytes responsible for transplant rejection. Therefore, it is essential to establish an appropriate therapeutic regimen, maintain therapeutic levels, and detect toxic levels. Objective To evaluate the interchangeability and degree of agreement in the quantitative determination of Tacrolimus in whole blood using two different analytical methods immunoassay (ACMIA) (Dimension® EXL™ 200; Siemens) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) (Nexera LC-40; Shimadzu - Triple Quad 5500+; SCIEX). Methods A total of 38 whole blood samples from patients, with values ranging from 0.5 to 10 ng/mL, were analysed. Measurements using ACMIA were performed on the same day as receipt, as part of routine procedures, while samples were stored at 4°C for subsequent analysis by LC-MS/MS. Both results were obtained following the manufacturers* instructions. For the comparative study, the MedCalc statistical software was used, and the Pearson correlation coefficient was calculated. Additionally, the non-parametric Passing-Bablok linear regression test and the Bland-Altman difference analysis were performed. Results In the Bland-Altman plot, the mean difference (Dm) between both measurements was -0.066% (95% CI -0.3174 to 0.1854). The Pearson correlation coefficient was r = 0.881 (95% CI: 0.785, 0.936). Passing-Bablok regression analysis: y = 0.16865 + 0.94000x. Intercept: 0.16865 (95% CI: -1.0090 to 0.8256): no constant systematic error observed. Slope: 0.9400 (95% CI: 0.7690 to 1.2468): no proportional systematic error observed. Conclusion In the Bland-Altman difference analysis, the confidence interval of the mean differences includes the value 0, indicating no significant differences between the results provided by both methods (p = 0.05). The slope is close to 1, indicating good proportionality between the methods, and the intercept is near 0, suggesting minimal systematic differences. In conclusion, the immunoassay and LC-MS/MS methods are comparable for Tacrolimus determination, with no significant systematic or proportional differences, suggesting that both methods are interchangeable within the analysed range.