In general, MU is comprised of many

In general, MU is comprised of many components specific to the sample. The uncertainty of an analytic result is influenced by three major phases of the determination: external operations (sampling technique, sample transport, storage temperature and time, and within-individual biologic variation), sample preparation (sub-sampling, sample preparation, and sample processing), and analysis (extraction cleanup, instrumental determination, assigned calibrator values, and calibration methods). Typically, a laboratory is only required to estimate the uncertainty associated with those processes over which it has control. There are two approaches to estimate MU: bottom-up and top-down [6]. The bottom-up approach is based on a comprehensive dissection of the measurement, whereby each potential source of uncertainty is identified and quantified. The identified uncertainties are then combined to generate a combined uncertainty using statistical propagation rules. The top-down approach directly estimates the MU for each measured value, typically by evaluating quality control (QC) data and method verification experimental data. According to expert opinion, MU estimates determined by top-down and bottom-up approaches should be interchangeable. Thus, clinical laboratories should be able to determine their own MUs using the simpler top-down approach [7, 8].