B-306 Performance Evaluation of an Automated Assay for Measurement of Tacrolimus* on the ADVIA Centaur XP System

Abstract

Abstract Background Tacrolimus (FK506) (PROGRAF) is a macrolide antibiotic of fungal origin (Streptomyces tsukubaensis). Tacrolimus is an inhibitor of calcineurin, a phosphatase that activates T-cell proliferation. At the cellular level, tacrolimus binds a family of binding proteins termed FK506-binding proteins (FKBPs). The correlation between steady-state trough concentration and area under the curve (AUC) provides reliable therapeutic monitoring for tacrolimus exposure at the trough level. The objective of this study was to determine the performance characteristics of the Tacrolimus assay on the ADVIA Centaur® XP System. Methods The ADVIA Centaur Tacrolimus assay is a competitive immunoassay using direct chemiluminescent technology. Free tacrolimus in the patient sample competes with the bound tacrolimus in the solid phase for binding with the acridinium ester-labeled anti-tacrolimus antibody. The amount of tacrolimus present in the patient sample has an inverse relationship to the amount of relative light units detected by the system. Results The ADVIA Centaur Tacrolimus assay demonstrated a mean %CV of 3.1% for intra-assay and 6.0% for total precision (across a sample range of 3.10 to 26.15 ng/mL). Close correlation to LC-MS/MS was demonstrated, with r, slope, and intercept of 0.957, 0.973, and 0.475, respectively. LoD and LoQ were 0.7 ng/mL and 1.9 ng/mL, respectively. Likewise, comparison to the Atellica IM assay resulted in r, slope, and intercept of 0.966, 1.09, and -0.508, respectively. Linearity was demonstrated across a range from LoQ to 30.0 ng/mL. Tacrolimus metabolite percent cross-reactivity ranged from 1.7 to 34.2%. A panel of potential interferants including the following were tested and found not to interfere (≤10%): cephalosporin to 100 µg/mL, erythromycin to 13.8 mg/dL, phenobarbital to 10 mg/dL, rapamycin to 5 µg/mL, sulfamethoxazole to 150 µg/mL, tobramycin to 3.3 mg/dL, trimethoprim to 4.2 mg/dL, bilirubin (conjugated) to 60 mg/dL, bilirubin (direct) to 60 mg/dL, and rheumatoid factor to 500 IU/mL. Conclusion The resulting data demonstrates that the ADVIA Centaur Tacrolimus assay is an accurate and precise method of quantifying tacrolimus concentration in EDTA whole-blood samples. *Assay under development by Randox Laboratories Ltd. for Siemens Healthineers. Not available for sale. Future availability cannot be guaranteed.