Uncertainty evaluation for the determination of repaglinide in human plasma by LC–MS/MS

Measurement uncertainty although introduced to medical laboratories some years ago, this concept is not familiar to all medical researchers, especially for the measurement of biological samples. Therefore, it is important to highlight the evaluation and expression of measurement uncertainty using a practical example. In accordance with published procedures for evaluating and expressing uncertainty, we analyzed the sources of uncertainty in the determination of repaglinide in human plasma using liquid chromatography–tandem mass spectrometry (LC–MS/MS). We investigated each component of uncertainty and calculated the combined and expanded uncertainties. We evaluated the uncertainty associated with repeatability, weighing, purity, solution and sample preparation, recovery, calibration fitting, and temperature. The expanded uncertainty for low, medium, and high concentrations of repaglinide was 0.090, 0.25, and 3.16 ng/mL, respectively (p = 95 %, k = 2). This example provides an important reference for the evaluation of uncertainty in biological sample determinations using LC–MS/MS and human plasma and will be helpful in explaining the reliability of test results.