B-320 Development of Two-step Sandwich CLEIA Kit for Tacrolimus With Automated Sample-Pretreatment Process, LUMIPULSE Presto® iTACT® Tacrolimus
Authors: Yamaguchi A , Funakoshi S , Iwashita C , Baba K , Sekiya S , Hirano Y , Hotta Y , Ise N , Moriyama K , Umeda K , Kaneko A , Aoyagi K 
Published: September 2023

Abstract

Background
Tacrolimus (The other name: FK506) is an immunosuppressive drug used for preventing rejection of allotransplantation and treating atopic dermatitis or rheumatoid arthritis. The complex consisting of Tacrolimus and FK506 binding protein binds to calcineurin and suppresses expression of Interleukin-2 (IL-2) and IL-2 induced immune response. Although tacrolimus is a useful immunosuppressive drug, this medicine causes serious side effects, such as renal dysfunction, opportunistic infections due to the excessive immunosuppression, and so on. Therefore, the measurement of the tacrolimus concentration in blood is required to obtain the maximum tacrolimus therapeutic effect without side effects. It is known that 95 percent of tacrolimus in blood localizes in the inside of erythrocyte, and this localization imposes cumbersome pretreatment process of whole blood. Almost all diagnostic reagents for tacrolimus need the manual whole blood pretreatment process that defaces the reliability of measurement values. And the existing diagnostic reagents often show the high cross-reactivity against the metabolite products of tacrolimus. To solve these inconveniences, we developed a highly-specific chemiluminescence enzyme immunoassay (CLEIA) for tacrolimus using a new automated sample-pretreatment process on a fully automated LUMIPULSE® L2400 analyzer. In this study, we report the basic performance of this new tacrolimus assay named as LUMIPULSE Presto® iTACT® Tacrolimus.

Methods
LUMIPULSE Presto® iTACT® Tacrolimus is the two-step sandwich CLEIA with the on-board sample-pretreatment process. All evaluations were executed on LUMIPULSE® L2400 analyzer (FUJIREBIO INC.). The on-board sample-pretreatment process is performed simultaneously with the first immune-reaction in sandwich CLEIA, and the total reaction time is 20 min. Limit of detection (LoD) and Limit of quantification (LoQ), within-run precision, day-to-day reproducibility, linearity, endogenous interferences, anticoagulative interferences, tacrolimus metabolites interferences and the correlation with current tacrolimus assay were evaluated in LUMIPULSE Presto® iTACT® Tacrolimus.

Results
Both of LoD and LoQ of LUMIPULSE Presto® iTACT® Tacrolimus were 0.12 ng/mL. Within-run precisions (% CVs) using three control samples were 0.4%–2.5%. Day-to-day reproducibility in five days were 0.4%–1.9%. We determined the linearity ranged from 0.29 to 48.80 ng/mL. Up to 19.7 mg/dL of conjugated bilirubin, 18.8 mg/dL of free bilirubin, 1620 FTU of chyle, 2000 mg/dL of triglycerides, 1000 IU/mL of RF, and 1010 ng/mL of HAMA, and 4–12 g/dL of proteins including albumin did not affect tacrolimus measurements. In addition, there was no influence by EDTA 2K and EDTA 2Na up to 10 mg/mL. The cross-reactivities of four tacrolimus metabolites (M-I, M-II, M-III, and M-IV) were respectively 0.4%–1.0%, 0.0%–0.8%, -0.7%–0.2%, and 0.7%–1.6%. Comparing to the existing chemiluminescence immunoassay (CLIA) with 128 specimens, the correlation coefficient was 1.0, and the slope calculated by Passing-Bablok method is 1.04. Comparing to the existing electrochemiluminescence immunoassay (ECLIA) with 137 specimens, the correlation coefficient was 1.0, and the slope calculated by Passing-Bablok method is 1.07.

Conclusion
The fundamental performance of LUMIPULSE Presto® iTACT® Tacrolimus is satisfactory and the on-board sample-pretreatment process of this assay is expected to contribute to reducing the burden and inconvenience of laboratory personnel.