title: Clinical evaluation of the QMS® Tacrolimus immunoassay.
abstract: BACKGROUND
  Tacrolimus, a widely used immunosuppressant, inhibits T-lymphocyte signal transduction and cytokine upregulation. We evaluated and compared the performance of a newly developed tacrolimus immunoassay method to LC-MS/MS.
  
  
  METHODS
  Analytical performance was assessed using quality control materials and whole blood patient samples. Interferences studies were performed using pooled whole-blood samples spiked with each interferent, respectively. Comparison studies were conducted using 145 de-identified whole blood samples collected after routine tacrolimus analysis by LC-MS/MS.
  
  
  RESULTS
  CVs were between 3.9 and 8.1% and the method was linear (r(2)=0.99) up to 30.0 ng/ml. Calibration was stable ≤12 days and LOQ was 0.7 ng/ml (14.4% CV). Bilirubin (≤48 mg/dl), hemoglobin (≤345 mg/dl), and triglycerides (<2800 mg/dl) showed no significant interference. Comparison (Passing-Bablok regression) for all samples showed a proportional bias of 17%. Comparisons of liver and kidney transplant patients showed slope biases of 22% and 31%, respectively, whereas other remaining transplant patients (stem cell, heart, lung, and islet) showed a slope bias of 0.98.
  
  
  CONCLUSIONS
  Overall, the QMS Tacrolimus Immunoassay showed good analytical performance. Comparison studies showed a proportional bias of 17%, which can be attributed to the significant number of liver and kidney transplant patients present in this study (121/145).
authors: Department of Pathology, Pritzker School of Medicine, The University of Chicago, Chicago, IL, United States. Electronic address: eleung1@bsd.uchicago.edu.
authors: Edward Ki Yun
authors: EK
authors: Leung
authors: Department of Pathology, Pritzker School of Medicine, The University of Chicago, Chicago, IL, United States.
authors: Xin
authors: X
authors: Yi
authors: Department of Pathology, Pritzker School of Medicine, The University of Chicago, Chicago, IL, United States.
authors: Carmelita
authors: C
authors: Gloria
authors: Department of Pathology, Pritzker School of Medicine, The University of Chicago, Chicago, IL, United States.
authors: Kiang-Teck J
authors: KT
authors: Yeo
mesh_terms: D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007166:Immunosuppressive Agents / Q000032:analysis*; D057230:Limit of Detection; D013058:Mass Spectrometry / Q000379:methods; D015203:Reproducibility of Results; D016559:Tacrolimus / Q000032:analysis*
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus
keywords: Immunoassay; Interference; LC–MS/MS; Method comparison; Tacrolimus