Preliminary evaluation of the new TACR flex method versus MEIA method in the therapeutic monitoring of tacrolimus in organ transplantation.

Tacrolimus (FK506) is an effective macrolide immunosuppressant widely used to prevent organ rejection following transplantation. Monitoring blood levels of tacrolimus is essential to assess organ rejection versus toxicity, because of the narrow therapeutic range and pharmacokinetic variability. The increased request for therapeutic drug monitoring is an interesting challenge for clinical laboratories. The automated immunoassay methods provide correct results and a turnaround time considerably reduced compared to HPLC and HPLC-MS which remain the gold standard for accuracy and economical advantages. A new immunoassay method, TACR Flex Dimension, is a commercially available, automated pretreatment test. The purpose of this study was to compare two analytical methods: the MEIA II tacrolimus immunoassay using the IMx analyzer and the new TACR Flex tacrolimus immunoassay on the Dimension system. Tacrolimus results obtained using the two methods were compared using European control and 93 whole blood samples from kidney and liver transplant patients. The tacrolimus concentrations measured by Flex Dimension for all samples were higher (0.7 to 16.1 ng/mL) than results obtained with MEIA (0.2 to 13.4 ng/mL), a mean difference expressed in percentage of 31.7%, and a correlation coefficient of 0.85. The data obtained by both methods using three European controls showed similar concentrations. The TACR Flex Dimension method provided a higher automation level and therefore a lower incidence of preanalytical errors and a lower turnaround time.