Clinical evaluation of the QMS® Tacrolimus Immunoassay

•The QMS tacrolimus immunoassay showed good overall analytical performance.•Comparison studies showed the overall proportional bias of 1.17.•Comparisons of liver and kidney transplant patients showed significant slope biases.•Comparison of other remaining transplant patients showed no slope bias.•Overall bias is due to more liver and kidney transplant patients in the study.

BackgroundTacrolimus, 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.MethodAnalytical 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.ResultsCVs were between 3.9 and 8.1% and the method was linear (r2 = 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.ConclusionsOverall, 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).