With increased awareness of metrological traceability, both from an IVD manufacturer and end-user perspective, improvements in analytical methods are possible. In this second article in his new series on measurement uncertainty, Stephen MacDonald provides a detailed overview of the issues involved.
Metrological traceability (MT) – 10 syllables in two words – can be a bit of a tongue twister but is central to all processes in the modern clinical laboratory. At its simplest it is a property of a measurement result that supports comparison and consistency.
It is not a new concept; thousands of years ago uniformity of the blocks used to construct the ancient pyramids was based around master blocks and units such as the cubit. The ability of sailors to navigate the globe was largely down to the traceability of the instruments used to measure and time their passage through rarely travelled areas. For us in the laboratory a result is only traceable if it is directly, through a chain of calibrations, related to a reference, with each step contributing to the final measurement uncertainty (MU).
A reference is a procedure or material that has a known and well-defined value, against which others can be compared. The procedure or material is used as the basis for calibration. That is achieved through a calibration hierarchy, allowing results between and within patients, for the same measurand, to be equivalent. This does not mean that they have to be identical; there will always be differences between results. However, those differences are to be managed within an acceptable tolerance, minimising risk of harm to the patient.
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