Metrology is the science of measurements and their applications. It deals with the measurements, systems of units and instruments used to make them. Based on the data obtained from the measurements made, decisions are taken. That is why it is very important that these data are reliable, reproducible and comparable between laboratories. The objective of metrology is to define and materialize the units of measurement and establishthe traceability chain. Traceability is the ability to relate the results of an individual measurement to national or international standards through an uninterrupted chain of comparisons, called the traceability chain. No measurement is completely accurate. Any type of instrument or equipment, even if it is used perfectly, can only record measurement with limited accuracy and precision. Therefore, every measurement has a degree of uncertainty, which indicates the quality of the result. In relation to health, if a measurement of achemical or biological component is inaccurate, it can have consequences and can even put human life at risk. Therefore measurements must be as accurate and precise as possible. Thanks to traceability, a laboratory is able to ensure that the measurements made have a certain degree of precision, because its standards are calibrated with more exact and precise standards, and so on until the standard materialized from a concept is reached. The further we move away from the primary standard, the degree of uncertainty associated with the result of a measurement increases. The results provided by the clinical laboratory must be accurate to allow a correct clinical interpretation and to be comparable with previous or subsequent results and between different laboratories. A measurement uncertainty can be attributed to each result. The uncertainty is a numerical expression of the degree of doubt of the result. When estimating the measurement uncertainty, an interval is established in which the true value of the measured quantity is found with a certain level of confidence.The importance of this issue lies in being able to provide reliable laboratory results, which allow to draw correct conclusions and take pertinent measures that will have repercussions on the health and therefore on the quality of life of patients.