Clinical evaluation of the QMS® Tacrolimus Immunoassay

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. Method: 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 (r²=0.99) up to 30.0ng/ml. Calibration was stable ≤12days and LOQ was 0.7ng/ml (14.4% CV). Bilirubin (≤48mg/dl), hemoglobin (≤345mg/dl), and triglycerides (<2800mg/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).